InsulationGuide
Types of Insulation

Types of Insulation Explained

There's no single "best" insulation. The right material for your home depends on where you're insulating, your climate, your budget, and how much of the work you want to take on yourself. This guide walks through every major type honestly — what it's made of, what it costs relative to the others, and the real pros and cons — so you can talk to a contractor (or take on a project yourself) with actual information instead of a sales pitch.

The Main Insulation Types

Five materials cover the vast majority of residential insulation projects. Each has a real place — the trade-offs are what matter.

Pink fiberglass batt insulation installed between wall studs

Fiberglass

DIY-friendly

Extremely fine strands of spun glass, sold as batts/rolls or as loose-fill for blown-in applications.

R-value/inch:
R-2.9 to R-3.8 per inch (batts); R-2.2 to R-2.7 per inch (blown-in loose-fill)
Relative cost:
$ (lowest cost tier)
Best for:
Standard stud-bay walls, attic floors, floors over unheated spaces.
  • Widely available and generally the least expensive option per square foot
  • Non-combustible and won't absorb moisture the way some organic materials can
  • Batts are cut to fit standard stud and joist spacing, making them approachable for a first DIY project
  • Doesn't seal air leaks on its own — gaps and compression reduce real-world performance well below the rated R-value
  • Fibers can irritate skin, eyes, and lungs during handling, so proper PPE matters
  • Lower R-value per inch than foam options, so it needs more depth to hit the same target
Blown-in cellulose insulation filling an attic floor between joists

Cellulose

DIY-friendly with a rented blower

Mostly recycled paper fiber (often 80%+ post-consumer newsprint), treated with borate compounds for fire and pest resistance.

R-value/inch:
R-3.2 to R-3.8 per inch (dense-packed or loose-fill, blown-in)
Relative cost:
$$
Best for:
Attic floors, retrofitting closed existing walls (dense-packed through small drilled holes), open new-construction wall cavities.
  • High recycled content and one of the more genuinely eco-friendly mainstream options
  • Settles into irregular spaces and around obstructions better than batts
  • Dense-packing does a reasonable job reducing air infiltration compared to loose fiberglass
  • Can settle and lose some loft (and R-value) over time if not installed at the right density
  • Absorbs and holds moisture more than fiberglass, which is a concern in humid climates or leak-prone areas
  • Blown-in equipment rental and cleanup add friction to a DIY attempt
A contractor spray-applying polyurethane foam insulation to a roof deck

Spray Foam

Professional-only

Liquid polyurethane components (a resin and an isocyanate) that react and expand on contact, curing into a rigid or semi-rigid foam.

R-value/inch:
Open-cell: R-3.5 to R-3.6 per inch. Closed-cell: R-6.0 to R-7.0 per inch.
Relative cost:
$$$ to $$$$
Best for:
Rim joists, hard-to-reach cavities, roof decks (unvented assemblies), and anywhere air sealing matters as much as R-value.

Open-cell vs. closed-cell, in short

Open-cell foam is softer, less expensive, and more vapor-permeable — often used on interior walls and roof decks where a vapor barrier isn't the goal. Closed-cell foam is denser, roughly double the R-value per inch, and acts as its own vapor barrier and rigid air/moisture seal — the usual choice for rim joists, below-grade walls, and tight cavities where every inch of depth counts.

  • Air-seals and insulates in a single step — no other material does both at once as effectively
  • Closed-cell foam has the highest R-value per inch of any common insulation, useful in space-limited cavities
  • Adds meaningful structural rigidity (closed-cell) and a degree of moisture resistance
  • The most expensive option per square foot by a wide margin
  • Mixing ratios, temperature, and application technique all have to be right — installation quality is the single biggest variable in how it performs and off-gasses
  • Once cured and covered, it's difficult and costly to remove if a problem is found later
Rigid foam board insulation panels installed against a foundation wall

Rigid Foam Board

DIY-friendly

Panels of expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (polyiso), cut to size and fastened or adhered in place.

R-value/inch:
R-3.8 to R-4.4 per inch (EPS/XPS); up to R-6 to R-6.5 per inch (polyiso)
Relative cost:
$$
Best for:
Basement and foundation walls, exterior continuous insulation, unvented low-slope roofs, garage doors.
  • High R-value per inch relative to fiberglass or cellulose, useful where wall depth is limited
  • Rigid panels are straightforward to measure, cut, and install with basic tools
  • Naturally resists moisture better than fibrous materials, which is valuable below grade
  • Seams between panels need to be taped or sealed or you lose much of the air-sealing benefit
  • Doesn't conform to irregular spaces or obstructions the way loose-fill materials do
  • Some types require a fire-rated cover (like drywall) when used on interior living spaces per code
Rock wool mineral wool insulation batts stacked for installation

Mineral Wool

DIY-friendly

Spun rock (basalt) or industrial slag fibers, sold as batts, rolls, or rigid boards.

R-value/inch:
R-3.0 to R-3.3 per inch
Relative cost:
$$$
Best for:
Fire-rated wall and floor assemblies, acoustic/soundproofing applications, standard stud walls.
  • Naturally fire-resistant — rock wool can withstand extremely high temperatures without supporting combustion
  • Denser than fiberglass, which makes it noticeably better at blocking sound transmission
  • Water-repellent and won't wick moisture the way cellulose can
  • Costs more than fiberglass for a similar R-value
  • Heavier and denser, which can make cutting and fitting slightly more physical work
  • Less widely stocked at big-box retailers than fiberglass, so sourcing can take extra steps

Specialty & Eco-Friendly Options

Beyond the five mainstream materials, a handful of specialty products come up regularly for homeowners who want lower VOCs, higher recycled content, or a specific performance edge.

Radiant Barrier

A reflective foil-faced material installed in attics to reflect radiant heat rather than absorb it. It doesn't add much R-value on its own, but in hot climates it can meaningfully reduce attic heat gain when paired with standard insulation underneath.

Sheep Wool

A natural fiber insulation that can absorb and release moisture without losing insulating performance, and it's naturally fire-resistant without heavy chemical treatment. It costs more than mainstream options and is harder to find locally.

Recycled Denim (Cotton)

Made from post-industrial cotton and denim scraps, treated with borate for fire and pest resistance. No fiberglass-style itch during handling and no VOCs, which makes it appealing for DIYers sensitive to standard batts — at a premium cost.

Choosing by Location

The right material often depends more on where in the house you're insulating than any single material's overall reputation.

Attic

The highest-ROI place to insulate in most homes. Blown-in cellulose or fiberglass are the most common choices for open attic floors; spray foam or rigid foam are used when the roof deck itself is being insulated (a "conditioned attic") instead of the floor.

Walls

New-construction or open walls take batts, blown-in loose-fill, or spray foam. Existing finished walls usually call for dense-packed cellulose or fiberglass blown in through small drilled holes — a job that's realistically professional territory.

Crawl Space

Moisture control matters as much as R-value here. Rigid foam board on the walls (as part of a sealed/encapsulated crawl space) is increasingly preferred over batts between the floor joists, which can sag and let air through over time.

Basement

Rigid foam board against foundation walls handles the moisture-prone below-grade environment better than fibrous batts. Closed-cell spray foam is a common upgrade where budget allows, since it insulates and air-seals masonry in one step.

Not sure how much R-value you need in each of these spaces? See the full R-value chart by climate zone →

Is Spray Foam Insulation Safe? Addressing the Reputation Questions Honestly

Spray foam has picked up a mixed reputation — some homebuyers walk away from listings that mention it, some insurers ask extra questions about it, and there are real stories of homes needing spray foam removed. Those concerns are legitimate, but the material itself isn't usually the root cause.

Installation quality is the actual variable that matters. Spray foam is a two-part chemical reaction happening on-site, in real time. If the mixing ratio is off, the substrate temperature is wrong, or ventilation during application is inadequate, the foam can cure improperly and off-gas longer than it should. Insurers scrutinize spray foam partly because improperly cured foam has caused real problems in a subset of homes — and partly because foam can hide roof decking or framing from a routine inspection, which is a legitimate concern regardless of how well the foam itself was applied.

None of that means spray foam is a bad material — closed-cell foam in particular remains one of the most effective air-sealing and insulating products available. It means the installer matters as much as the product. A correctly mixed, properly ventilated, code-compliant spray foam job performs exactly as intended and doesn't carry the risks associated with the horror stories.

This is exactly why vetted, insured installation matters.

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Does insulation reduce noise?

Yes, to a degree — though R-value and sound-blocking (measured separately as STC, or Sound Transmission Class) aren't the same thing. Density is what matters most for noise, which is why mineral wool and dense-packed cellulose outperform standard fiberglass for acoustic purposes even at a similar R-value. If soundproofing is your main goal (a shared wall, a home office, a media room), factor that in separately from the R-value target.

Quick Comparison

Everything above, in one place.

MaterialR-Value / InchDIY-FriendlyRelative CostBest For
Fiberglass BattsR-2.9–R-3.8Yes$Standard stud cavities, budget-conscious projects
Cellulose (Blown-In)R-3.2–R-3.8Yes (rented blower)$$Attic floors, retrofitting closed walls
Open-Cell Spray FoamR-3.5–R-3.6No$$$Air sealing, roof decks, interior cavities
Closed-Cell Spray FoamR-6.0–R-7.0No$$$$Rim joists, tight cavities, below-grade walls
Rigid Foam BoardR-3.8–R-6.5Yes$$Basements, exterior continuous insulation
Mineral WoolR-3.0–R-3.3Yes$$$Fire-rated assemblies, soundproofing

Want real dollar figures instead of relative cost tiers? See the full cost breakdown →

Frequently Asked Questions

There's no single best choice — for an open attic floor, blown-in cellulose or fiberglass are the most common and cost-effective options because they settle around joists and obstructions easily. If you're insulating the roof deck itself (a conditioned attic), spray foam or rigid foam board is more typical because the space works differently.

It depends on the application and your budget. Spray foam costs significantly more per square foot than fiberglass or cellulose, but it air-seals and insulates in one step and has the highest R-value per inch of any common material. It tends to be worth the premium in tight or leak-prone spaces (rim joists, roof decks, additions) rather than as a blanket choice for an entire home.

Fiberglass batts and rigid foam board are generally the most approachable for a homeowner, since they're precut or easily cut with basic tools and don't require specialized equipment. Blown-in cellulose or fiberglass is doable with a rented blower for a straightforward attic top-up. Spray foam is not a realistic DIY project for most homeowners.

Neither is universally better. Fiberglass is typically less expensive and won't absorb moisture, while cellulose has higher recycled content, packs more densely (helping with air sealing), and fills irregular spaces well. In practice, many installers choose based on the specific application, local pricing, and climate rather than a fixed preference.

Any insulation reduces some sound transmission compared to an empty wall cavity, but density matters most for acoustic performance. Mineral wool is generally the strongest standard option for blocking noise, with dense-packed cellulose a reasonable second choice.

Keep Going

Understanding R-Value

What that number means and how much you actually need.

Insulation Cost & ROI

Real cost ranges by material and by project.

DIY vs. Professional

Which of these materials you can realistically install yourself.

Not Sure Which Material Is Right for Your Home?

A vetted, insured local contractor can assess your space and recommend the right material for your climate, budget, and goals — no pressure, no obligation.

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