What is a REScheck? And why it matters in Connecticut

Let’s get one thing straight—there’s no universal “best attic insulation” for every home. That’s like asking what the best pair of shoes is without knowing if you’re running a marathon or going to a wedding. The right insulation depends on your attic, your climate, your budget, and—frankly—how long you plan on sticking around.

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But here's what we can say: the attic is one of the biggest culprits when it comes to energy loss. Heat loves to rise, and without proper insulation up top, your home is basically wearing a winter coat with no hat. That means higher energy bills, drafty rooms, and HVAC systems working harder than they should.

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In this guide, we’ll break down the most popular attic insulation materials—fiberglass, cellulose, spray foam, mineral wool—compare their strengths, costs, and R-values, and help you figure out what’s actually worth your money in 2025. Whether you’ve got a new build, a 100-year-old shoreline cape, or just a suspicion your attic's slacking off, this post is for you.

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Let’s dig into what makes insulation great—and how to choose the right kind for your home.

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What Makes Insulation ‘The Best’ for Your Attic?

Before we start comparing cellulose to spray foam like it’s a heavyweight title fight, let’s set the bar: what actually makes one attic insulation material better than another?

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Here’s what we look at when choosing the best attic insulation:

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R-Value (Thermal Resistance)

Think of R-value like the “warmth rating” on a sleeping bag. The higher the number, the better it resists heat transfer. In New England, you want an attic R-value between R-49 and R-60, depending on your setup and climate.

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Air Sealing

Insulation slows down heat, but air sealing stops the drafts. Spray foam is the gold standard here—it does both. Dense-pack cellulose can help too. Fiberglass? Not so much.

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Moisture Resistance

Insulation that soaks up moisture is asking for mold. If your attic lacks proper ventilation or has humidity issues, pick something that holds up—like closed-cell spray foam or mineral wool.

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Longevity and Settling

Insulation is a “set it and forget it” kind of job—if it’s installed right. Spray foam holds its shape. Cellulose and fiberglass can settle if installed too lightly. Batt insulation? Depends on who installs it.

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Cost vs. Performance

Spray foam has the highest performance—and the highest price. Cellulose hits the sweet spot for cost, coverage, and comfort. Fiberglass is cheap, but often leaves performance on the table.

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👉 Bottom line: The “best” insulation is the one that fits your attic’s needs, not just your wallet.

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The Main Types of Attic Insulation (Pros, Cons & What to Expect)

There’s no shortage of options, but these five are the ones we see most in Connecticut attics—and each one has its quirks.

Here’s the no-BS breakdown:

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Blown-In Fiberglass

Pros: Affordable, quick install, moderate R-value (R-2.2 to R-2.7)
Cons: No air sealing, moisture-sensitive, settles over time
Best for: Open attics with good airflow and low moisture risk

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Dense-Pack Cellulose

Pros: High R-value (R-3.2 to R-3.8), air sealing capability, pest/mold/fire resistant, eco-friendly
Cons: Can settle if under-packed, doesn’t like moisture
Best for: Older homes, retrofits, irregular cavities

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Spray Foam (Closed Cell)

Pros: Highest R-value (up to R-7), air seals, moisture barrier, long-lasting
Cons: Expensive, must be professionally installed
Best for: Rim joists, vaulted ceilings, hard-to-reach areas

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Fiberglass Batts

Pros: Cheap, easy to install (DIY-friendly), decent R-value
Cons: Poor fit = poor performance, no air sealing, vulnerable to compression
Best for: Simple, accessible attics with standard joist spacing

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Mineral Wool

Pros: Good R-value (R-4+), fireproof, water-resistant, soundproof
Cons: More expensive than fiberglass, harder to find
Best for: Moisture-prone or fire-rated assemblies

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Attic Insulation Comparison Table

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Best Attic Insulation for Different Situations

Let’s match the material to the attic:

• Cold Climates: Closed-cell spray foam or dense-pack cellulose. Seal the leaks, then insulate deep.
• Humid Climates: Radiant barrier plus fiberglass or open-cell foam.
• Older Homes: Dense-pack cellulose + foam at rim joists and access points.
• New Construction: Closed-cell spray foam or hybrid (foam + cellulose).
• DIY Projects: Fiberglass batts or rental cellulose blower kits (if you know what you're doing).

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Bottom line: Match the insulation to your home—not the other way around.

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What R-Value Do You Really Need in Your Attic?

In Connecticut, aim for R-49 to R-60 in your attic. If you already have R-19, you can add to it.

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R-Value by Material (Per Inch)

• Blown-in fiberglass: R-2.2 to R-2.7 → ~18-22 inches needed
• Cellulose: R-3.2 to R-3.8 → ~13-15 inches
• Open-cell foam: R-3.5 to R-4.0
• Closed-cell foam: R-6 to R-7
• Mineral wool: R-4 to R-4.2

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And don’t forget: Air sealing comes first. Always.

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Common Attic Insulation Mistakes (And How to Avoid Them)

Let’s save you the expensive redo:

• Skipping air sealing: Insulation without sealing is like socks in wet shoes—pointless.
• Choosing solely on price: The cheapest option often costs more in the long run.
• Ignoring ventilation: You need airflow, or you’ll end up with mold.
• Reusing old insulation: If it’s saggy, moldy, or mouse-nested—remove the insulation.
• Leaving the hatch uninsulated: Your attic access is a massive weak point. Seal it tight.

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So… What’s the Verdict?

If you’re just looking for the straight answer:

• Best all-around: Dense-pack cellulose
• Best performance: Closed-cell spray foam
• Best combo: Foam for air leaks + cellulose for coverage

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Common FAQ's about Attic Insulation

How do I know if my attic insulation needs to be replaced?

You should replace attic insulation if it's sagging, wet, moldy, chewed by pests, or over 20–30 years old. Rising energy bills, drafts, or uneven room temperatures are also warning signs. Poor installation, moisture, or critters can shorten insulation life—if it's never been inspected, it's likely due for a checkup.

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Can I add new insulation on top of the old stuff?

You can add new insulation over old material if it's dry, mold-free, and not compacted. This method is cost-effective and helps meet attic R-value codes. However, if the old insulation is damp, damaged, or pest-infested, it should be removed first to avoid trapping moisture or odors.

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How long does attic insulation typically last?

Attic insulation typically lasts 20–30 years if installed properly and kept dry. Spray foam can last even longer. Moisture, pests, and settling can shorten its lifespan. If you notice uneven temperatures or higher energy bills, it’s smart to have your attic insulation checked every 10–15 years.

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Will new attic insulation qualify me for rebates or tax credits?

Yes, new attic insulation can qualify for rebates and tax credits in Connecticut. Programs like EnergizeCT and the federal Inflation Reduction Act offer incentives for energy-efficient upgrades. To qualify, you’ll need proper documentation, including receipts and possibly a home energy assessment, typically submitted by your contractor.

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Conclusion: Insulation Is an Investment—Do It Right

Insulation isn’t sexy, but it saves you money, boosts comfort, and protects your home from the elements. Get it right the first time, and you won’t have to think about it again for 30 years.

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👉 Want an expert to take a look at your attic? Contact us today. We’ll help you figure out what actually makes sense for your attic—not just what’s on sale.

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If you’ve ever walked into your basement after a rainy week and caught a whiff of that musty, damp smell—you already know why moisture resistance matters. Insulation isn’t just about keeping warm in the winter or cool in the summer. It’s also your home’s first line of defense against hidden water damage, mold, and air quality issues.

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That brings us to a common showdown in the insulation world: blown-in fiberglass vs spray foam moisture resistance. Both materials get tossed around as “energy-saving” upgrades, but only one holds its ground when things get wet.

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In this post, we’re breaking down how each insulation type performs when moisture enters the picture—whether it’s humid air, condensation, or a good ol’ New England nor’easter working its way through your walls. We’ll compare absorption rates, mold resistance, and where each one works best in a real Connecticut home.

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Let’s get into it.

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Understanding Moisture Resistance in Insulation

When we talk about moisture resistance in insulation, we mean how well a material handles water—whether from a leaky roof, humid summer air, or condensation inside your walls.

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Why does that matter? Because moisture is the silent killer of comfort and efficiency. It soaks into your insulation, wrecks its R-value, invites mold, and can even rot out your framing. If your insulation acts like a sponge, you’re basically paying to heat or cool a pile of mildew.

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Good moisture resistance means:

• No soggy insulation dragging down performance
• Less risk of mold and mildew
• Better indoor air quality
• A longer-lasting thermal barrier

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Whether you’re insulating an attic in Guilford or a crawl space in Old Saybrook, understanding how different materials deal with moisture can save you a serious headache down the line.

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Blown-In Fiberglass: Pros and Cons for Moisture

Blown-in fiberglass is the fluffy white stuff you’ll see in attics or walls—lightweight, quick to install, and relatively affordable. But here’s the catch: it’s not built to handle moisture.

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The Moisture Problem

Fiberglass doesn’t exactly invite mold, since it’s not organic. But it does absorb and hold moisture, which creates the perfect damp, musty environment mold loves. Once it gets wet, fiberglass insulation:

• Loses R-value (up to 50%)
• Slumps or settles in cavities
• Traps moisture against wood framing
• Can make your attic or basement smell like a gym bag

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We’ve seen it all over Connecticut—moisture issues with fiberglass insulation are common in homes with poor air sealing, roof leaks, or just a little too much summer humidity.

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Where It Can Work

To be fair, blown-in fiberglass does just fine in dry, ventilated spaces—think attics with plenty of airflow and no risk of leaks. But in moisture-prone areas, like basements, crawl spaces, or rim joists? It’s not the material you want in your corner.

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Spray Foam Insulation: Pros and Cons for Moisture

Now let’s talk spray foam—the tough, no-nonsense cousin of fiberglass. It expands to seal every crack, crevice, and air leak. And when it comes to moisture? Especially closed-cell spray foam? It’s in a different league.

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Closed-Cell = Moisture Barrier

Closed-cell spray foam is dense and rigid—and doesn’t absorb water. It acts as its own vapor barrier, meaning it prevents moisture from getting in at all.

That means:

• No soaking, sagging, or slumping
• No mold growing behind the walls
• No hidden condensation issues
• Bonus: it adds structural strength

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It’s the go-to choice for wet basements, crawl spaces, rim joists, or any area where moisture is a concern. It’s also ideal for Connecticut’s humid summers and snowy winters.

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What About Open-Cell?

Open-cell spray foam is cheaper and more flexible, but it’s not water-resistant. It can absorb moisture, and it won’t block vapor movement the way closed-cell does. Not a great fit for moisture-prone areas.

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Does Spray Foam Prevent Condensation?

Yes—closed-cell spray foam can actually help prevent condensation by sealing air leaks and eliminating the cold surfaces where water vapor would otherwise collect.

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Head-to-Head Comparison: Fiberglass vs Spray Foam

Here’s how these two stack up side by side:

Bottom line: fiberglass can work if you control the moisture. But spray foam controls it for you.

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Choosing the Right Insulation for Moisture-Prone Areas

So how do you actually choose the right insulation? Here’s how we do it in the field:

1. Where’s it going?

• Dry attic? Fiberglass may work just fine.
• Basement, crawl space, or anywhere with moisture risk? Spray foam wins.

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2. What’s the climate?

Connecticut throws us heat, humidity, snow, and wind. That means your insulation needs to block moisture and air leaks year-round.

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3. What’s the structure like?

Older homes with uneven framing? Weird little rim joists? Spray foam seals tight, even in tough spots where fiberglass fails.

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4. What’s your budget—and your risk tolerance?

Fiberglass costs less up front but may need replacing if it gets wet. Spray foam costs more but lasts decades and protects from the start.

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Common FAQ's About Fiberglass, Spray Foam and Moisture

Can I mix blown-in fiberglass and spray foam in different areas of my home?

Yes, you can mix blown-in fiberglass and spray foam in different areas of your home. Spray foam works best in damp or draft-prone spaces like rim joists and crawl spaces, while blown-in fiberglass is ideal for open, dry attics. Using both balances performance, air sealing, and cost efficiency.

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Will moisture-resistant insulation help with musty smells in my basement?

Yes, moisture-resistant insulation helps reduce musty basement smells by blocking damp air and preventing condensation. Closed-cell spray foam seals rim joists and walls, keeping moisture out. When combined with air sealing and ventilation, it stops mold and mildew that cause odors and creates a drier, fresher space.

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How can I tell if my current insulation has moisture damage?

Check for moisture damage in insulation by smelling for musty odors and looking for sagging, clumped, discolored, or moldy material. In fiberglass, moisture causes settling or compression. Rising energy bills or drafts can also signal trouble. Professionals use thermal cameras or moisture meters to confirm hidden damage.

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Do I need a vapor barrier if I use spray foam?

You need a vapor barrier only if you're using open-cell spray foam. Closed-cell spray foam acts as its own vapor barrier due to its density and moisture resistance. Open-cell spray foam allows vapor through, so a separate vapor barrier is often required—especially in basements and crawl spaces in Connecticut.

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Is moisture-resistant insulation worth the higher cost?

Moisture-resistant insulation is worth the higher cost in damp areas. Closed-cell spray foam offers insulation, air sealing, and vapor protection in one, preventing mold, rot, and future repairs. Though more expensive upfront, it delivers long-term savings, better energy efficiency, and improved indoor air quality—making it a smart investment in moisture-prone zones.

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Final Verdict: Which Insulation Handles Moisture Better?

If moisture’s your concern—and let’s face it, it should be—closed-cell spray foam is your best bet. It blocks water, seals air, adds structure, and keeps you comfortable no matter what’s happening outside.

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Blown-in fiberglass has its place, but only in dry, predictable environments. In damp or risky areas, it just doesn’t cut it.

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Still not sure? Most insulation problems we see come from good intentions—but the wrong material in the wrong place. That’s why it pays to get it right the first time.

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👉 Need help figuring out the right insulation for your home? We’ve been insulating Connecticut homes since 1977, and we know what holds up to the elements—and what doesn’t. Let’s talk.

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Let’s get one thing out of the way: insulation isn’t sexy. But you know what is? Lower energy bills, a more comfortable home, and not hearing your HVAC wheeze like it’s running a marathon.

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If your attic is under-insulated—or insulated with the wrong stuff—you’re basically paying to heat the outdoors. And in Connecticut, where the seasons come in hot and cold (literally), that’s a losing game.

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So which attic insulation type actually delivers when it comes to energy efficiency? Let’s break it down.

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What Makes Insulation “Energy Efficient,” Anyway?

Let’s get one thing straight: energy-efficient insulation isn’t just about stuffing something fluffy in your attic and hoping for the best. It’s about controlling how heat moves through your home—and more importantly, how to stop it from escaping like a dog that figured out the screen door.

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The first thing folks bring up is R-value. That’s the measurement of how well a material resists heat flow. Higher R-value = better insulation performance. But here’s the kicker: R-value alone doesn’t tell the full story.

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Imagine wearing a thick winter coat full of holes. That’s high R-value with bad air sealing. Doesn’t matter how “warm” the material is if drafts are whistling right through it. That’s why air sealing is the unsung hero of insulation. A well-sealed attic paired with the right material will keep your home warmer in winter, cooler in summer, and your HVAC system from running a marathon every day.

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Another piece people overlook? Moisture control. Insulation that gets damp (looking at you, open fiberglass batts in a leaky attic) won’t perform well for long. And in a Connecticut climate, where humidity swings like a mood on Monday morning, that stuff matters.

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So when we talk about energy-efficient insulation, we’re looking for:

• High R-value (per inch, especially in tight attic spaces)
• Strong air sealing (no sneaky drafts)
• Moisture resistance (so performance stays strong over time)

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In short, the best insulation for energy efficiency does more than sit there. It seals, insulates, and holds up to weather, time, and the messiness of real life.

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Comparing the Main Types of Attic Insulation

Alright, now that we know what actually makes insulation energy efficient, let’s talk about your options. Not all insulation is created equal—and each type brings something different to the table. Some are air-sealing ninjas. Others are more like paper towels: cheap, common, and not great under pressure.

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Here’s the plain-English breakdown.

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Spray Foam Insulation (Open-Cell & Closed-Cell)

The Cadillac of attic insulation. Spray foam is high-performance and high-budget—and for good reason.

• Closed-cell spray foam has the highest R-value per inch (around R-6 to R-7), acts as an air and vapor barrier, and basically hardens into a weatherproof seal. It’s ideal for tight, irregular spaces or when you need max performance in minimal depth.
• Open-cell spray foam is softer, cheaper, and still seals air leaks—but it absorbs moisture like a sponge, so we don’t recommend it below-grade or in humid Connecticut attics.

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Best for: Energy efficiency, homes with weird attic geometry, or when air sealing is non-negotiable
Downside: Expensive, and it’s not a DIY weekend warrior kind of job

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Blown-In Cellulose Insulation

The workhorse. Cellulose is recycled newspaper treated with borates (which handle mold, fire, and pests like a bouncer at the door). It’s dense, it fills every nook, and it’s one of our go-to choices in Connecticut homes.

• R-value sits around R-3.5 to R-4 per inch
• Blown in over attic floors or dense-packed into rafter bays, it settles in tight and stops air movement better than fiberglass
• It’s also eco-friendly and cost-effective—without being flimsy

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Best for: Retrofitting older homes, topping off existing insulation, and environmentally conscious upgrades
Downside: Needs proper air sealing underneath to shine. Can settle slightly over time if not dense-packed

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Fiberglass Batt Insulation

The old standby. You’ve seen fiberglass: pink or yellow rolls shoved between attic joists. It’s cheap and easy to install, which is why it’s everywhere—but that doesn’t mean it’s the most efficient.

• R-value ranges from R-2.9 to R-3.8 per inch
• Doesn’t seal air gaps at all—so unless it’s paired with perfect air sealing, heat escapes right around it
• Works better in open spaces with standard joist spacing and minimal obstacles

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Best for: New builds on a budget, wide-open attic spaces
Downside: Gaps, drafts, and poor performance in real-world conditions if not installed carefully

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Each of these materials has its place. But if you're chasing real energy efficiency in your attic—especially in the unpredictable climate we get here in Connecticut—you want to pick the one that does more than just check the R-value box. You want something that actually seals, resists moisture, and lasts.

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Energy Efficiency Comparison Table: The Good, The Better, and The Drafty

Now that we’ve walked through the big three insulation types, let’s put them head-to-head in a no-fluff comparison. Because at the end of the day, you’re probably asking: “Which one gives me the most bang for my buck?”

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Mike’s Take:

• Want top-tier efficiency with the budget to match? Closed-cell spray foam is hard to beat. It insulates and air seals in one shot.
• Want real performance without breaking the bank? Dense-packed cellulose gives great results—especially when paired with proper air sealing.
• Looking at batts or open-cell foam in a Connecticut attic? You might save upfront, but you’ll likely pay it back (and then some) on your energy bills.

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Bottom line: The best attic insulation for energy efficiency isn’t just about R-value—it’s about how well it works in real homes, through real winters, with real utility bills on the line.

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What’s the Best Attic Insulation for Connecticut Homes?

Let’s narrow it down. Because while charts and specs are nice, you’re not insulating a lab—you’re insulating a house in Connecticut, where winter winds can rattle your windows and summer humidity turns your attic into a sauna.

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For Older Connecticut Homes

Most of the houses we work on—especially along the shoreline—are 50+ years old, drafty as a barn, and built long before energy efficiency was a thing. If that sounds like your place, blown-in cellulose is usually the sweet spot.

• It settles into every nook and cranny in your attic floor
• It plays well with uneven framing and weird attic shapes
• When dense-packed, it seals up air leaks surprisingly well—especially when combined with attic air sealing and baffles

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It’s also green, affordable, and it won’t attract pests or mold if installed correctly. We've installed it in homes from Branford to Old Saybrook, and it’s made a night-and-day difference.

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For Homes with Moisture Concerns or Complex Rooflines

If your attic looks more like a jungle gym of trusses or you’ve had issues with condensation, damp rafters, or ice dams, closed-cell spray foam is the better long-term play.

• It offers both insulation and a vapor barrier
• It locks in heat and blocks moisture from the roof deck down
• It’s pricier, but in the right situation, it can save you thousands in energy loss and roof repairs

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Perfect for homes where you're insulating under the roof deck (cathedral ceilings, conditioned attics, etc.) or when you want your attic space within the thermal envelope.

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What We Don’t Recommend

• Open-cell spray foam? Skip it in unvented attics here—it absorbs moisture like a sponge and can lead to rot.
• Fiberglass batts? They’re fine in new builds but don’t hold up well in real-world conditions. Gaps, compression, and air leakage are all too common.

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So What’s “Best”?

If we’re talking about the best attic insulation for energy efficiency in Connecticut, the real answer is: it depends on your house. But most of the time, it comes down to dense-packed cellulose for cost-effective upgrades, or closed-cell spray foam for max performance in moisture-prone or complex spaces.

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Final Verdict: What’s the Most Energy-Efficient Attic Insulation?

If you’ve stuck with me this far, you now know more about attic insulation than most contractors on Facebook Marketplace. So let’s cut to it:

• Want top-tier efficiency with the budget to match? Go with closed-cell spray foam. It insulates, seals, and shrugs off moisture like a champ.
• Want serious performance without torching your wallet? Dense-packed cellulose is the MVP—especially in older, drafty New England homes.
• Looking at fiberglass batts or open-cell foam for your attic? Be cautious. They have their place, but that place isn’t usually in a Connecticut attic.

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Remember, the “best” insulation isn’t just about R-value—it’s about how it performs in your home, with your roof, and your climate. That’s why we don’t do cookie-cutter solutions. We do what works.

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And what works? Quality materials, smart air sealing, and an installer who knows the difference between cutting corners and doing it right.

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👉 Want us to take a look at your attic and lay out the smartest path forward? Contact Nealon Insulation and let’s make your home more efficient, comfortable, and quiet—without the guesswork.

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Common Attic Insulation FAQ's

How do I know if my attic is under-insulated?

You can tell your attic is under-insulated if rooms are hard to heat or cool, ice dams form in winter, or the insulation looks thin, patchy, or dusty. Seeing exposed joists is another red flag. In Connecticut, attics should meet R-49 to R-60. A professional audit confirms insulation levels.

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Can I mix different types of attic insulation?

You can mix attic insulation types, like adding cellulose over fiberglass, if the existing material is dry, stable, and air sealing is completed first. Mixing requires care—done improperly, it can trap moisture or reduce performance. Consult a pro to ensure compatibility and code compliance.

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Does adding attic insulation qualify for any rebates or tax credits?

Yes, adding attic insulation may qualify for rebates or tax credits. In 2025, the federal Energy Efficient Home Improvement Credit offers up to 30% back (up to $1,200) for qualifying upgrades. Connecticut homeowners may also receive additional rebates through Energize CT based on utility provider and income.

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How long does attic insulation typically last?

Attic insulation typically lasts 20–30 years if installed properly and kept dry. Cellulose maintains performance well over time, while fiberglass may settle or degrade. Spray foam can last the lifetime of the home if protected from UV exposure and moisture. Longevity depends on material type and environmental conditions.

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Will insulating my attic reduce noise too?

Yes, insulating your attic can reduce noise. Dense materials like cellulose and spray foam absorb sound, helping to block outside noise such as rain or reduce indoor noise like HVAC equipment. While thermal performance is the main benefit, attic insulation also improves home acoustics and quietness.

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