Best Attic Insulation: Batts, Blown-In, Foam and Radiant Barrier

Which insulation suits your attic floor or rafters, the R-value you are aiming for, and the air sealing and baffles that make it work.

The best attic insulation is the one that reaches your target R-value in the space you have, without blocking the soffit vents that keep the roof deck dry. On an open attic floor that usually means topping up with blown-in or unfaced batts laid across the joists; in a cathedral ceiling or a finished attic it means high-density batts or foam between the rafters.

Below, each type is compared by what it is for and the one specification to read, and the depth you need is worked out with the same function as our insulation calculator — for a 1,200 sq ft attic going from R-19 to R-49.

Compared by type

Pros and cons describe each type from its specifications; this is not a hands-on product test. As an Amazon Associate we earn from qualifying purchases.

Fiberglass batts and rolls (unfaced)

Best for: Topping up an open attic floor, laid across the existing joists. Check: The R-value and width on the bag — match 16 in or 24 in joist spacing.

Pros

Easy for one person to carry into an attic and cut with a knife
Unfaced rolls lay straight over old insulation with no vapour-barrier conflict
Widely stocked in R-19, R-30 and R-38

Cons

Gaps and compression cut the real R-value — it must be fitted snugly, not stuffed
Itchy to handle; long sleeves, gloves and a respirator are needed
Slower than blowing in over irregular joists and obstructions

Mineral wool (stone wool) batts

Best for: Rafter bays, knee walls and areas near chimneys and recessed lights rated for contact. Check: R-value per batt and whether it is sized for 16 in or 24 in framing.

Pros

Slightly higher R per inch than fiberglass batts, and holds its shape friction-fit
Non-combustible and highly fire resistant
Does not sag in vertical knee walls

Cons

Heavier and costs more per square foot than fiberglass
Fewer thicknesses stocked, so deep attic floors take several layers
Still needs baffles to keep soffit vents open

Radiant barrier foil

Best for: Hot, sunny climates where the attic holds ductwork. Check: Perforated (breathable) vs solid foil, and the emissivity figure.

Pros

Reflects radiant heat from the roof deck before it reaches the attic floor
Light and quick to staple to the underside of rafters
Works alongside existing insulation rather than replacing it

Cons

Adds little in cold climates, where heat loss is by conduction
Dust on a face-up foil stops it working — staple it to the rafters
Solid foil laid on the floor can trap moisture; use perforated

Rigid foam board (polyiso, XPS, EPS)

Best for: Attic hatch covers, knee-wall backs and the underside of rafters in finished attics. Check: R per inch and whether the facer is foil (radiant) or plain.

Pros

Highest R per inch of the DIY options (polyiso especially)
Doubles as an air barrier when the seams are taped
Stiff enough to build an insulated hatch or stair cover

Cons

Awkward to fit between irregular framing
Most codes require it to be covered by a thermal barrier in living spaces
Too expensive to cover a whole attic floor

Rafter vent baffles

Best for: Every vented attic before adding insulation near the eaves. Check: Width for your rafter spacing and length to clear the insulation depth.

Pros

Keep a clear air channel from the soffit vents to the roof deck
Stop blown insulation spilling into the soffits
Inexpensive and fast to staple in

Cons

Working at the eave is the most cramped part of the attic
Needed in every bay, so counts add up on a long house

Spray foam sealant (cans and kits)

Best for: Air sealing top plates, wiring holes and plumbing penetrations before insulating. Check: Gap size on the can, and fire-block rating where codes require it.

Pros

Air sealing makes every inch of insulation above it work harder
A can reaches holes that batts cannot seal
Fire-block versions are made for penetrations between floors

Cons

Expanding foam can bow thin materials — use the minimal-expansion type around frames
Two-part kits are expensive and need careful temperature control
Does not replace bulk insulation

What R-value to aim for

ENERGY STAR recommends R-49 to R-60 for an uninsulated attic in most of the northern half of the US (climate zones 4 to 8) and R-30 to R-60 in warmer zones; your local code sets the minimum for new work. If you already have some insulation, add only the difference. The insulation calculator does this; the example below uses the same function.

Worked example: A 1,200 sq ft attic floor from R-19 to R-49

R-value to add: 49 − 19 = R-30
Area with 5% waste: 1,260 sq ft
Blown cellulose at about R-3.2 per inch → 9.4 in added depth
Blown fiberglass at about R-2.5 per inch → 12 in
Fiberglass batts at about R-3.1 per inch → 9.7 in; mineral wool at about R-3.3 → 9.1 in

Plan on roughly 9.1–12 inches of new insulation over the whole floor, depending on the material — and check the bag's own coverage chart before counting bags or rolls.

Depth matters at the eaves too: the roof slope leaves less room there, which is why baffles go in first. See the roof insulation guide for vapour retarders, and the attic ventilation calculator to check your soffit intake before covering anything.

Which type goes where

Attic insulation by location (R per inch is typical, check the product)
Location	Usual choice	Typical R per inch	Why
Open attic floor, top-up	Blown-in or unfaced batts across the joists	2.5–3.7	Covers the joists and fills around obstructions
Around the hatch	Rigid foam cover plus weatherstrip	4–6.5	The hatch is often the biggest single leak
Rafters in a finished attic	Mineral wool or high-density batts plus foam	3.3–6.5	Limited depth; needs the highest R per inch
Eaves	Rafter baffles, then insulation	—	Keeps soffit air flowing to the deck
Underside of the roof deck (hot climates)	Perforated radiant barrier	—	Blocks radiant heat, adds no R-value itself
Top plates and penetrations	Spray foam and caulk	—	Air sealing before insulating

What to look for on the listing

Unfaced for top-ups. Adding a second paper or foil facing on top of existing insulation traps moisture between the layers.
Width to match your framing. Batts come for 16 in and 24 in spacing; the wrong width leaves gaps or gets compressed.
Coverage per bag or roll, stated at a given R-value. Compare the square feet each package covers at your target R, not the price per bag.
Contact ratings around lights. Only IC-rated recessed fixtures may be covered; keep the required clearance from chimneys and flues.
Safety gear. Long sleeves, gloves, eye protection and a respirator are needed for fiberglass, mineral wool and blowing cellulose.

Safety notes

Walk only on the joists or on boards laid across them; stepping between joists puts a foot through the ceiling.
Keep insulation the required distance from chimneys, flues and non-IC light fixtures, and never cover knob-and-tube wiring.
Attics get dangerously hot in summer — work early in the morning and take breaks.
Wear a respirator rated for fibres, eye protection and long sleeves when handling fiberglass, mineral wool or cellulose.

Frequently asked questions

What is the best insulation for an attic?

For an open attic floor, blown-in cellulose or fiberglass, or unfaced fiberglass batts laid across the joists, are the usual choices because they cover the joists and fill around obstructions. In a finished attic or cathedral ceiling, mineral wool or high-density batts combined with rigid foam give the most R-value in limited depth.

Is blown-in or batt insulation better for an attic?

Blown-in fills around wiring, bracing and irregular joists with fewer gaps, which is why it is common for top-ups. Batts are easier to handle without a machine and work well when the joists are regular. Either reaches the same R-value if it is installed without gaps or compression.

How much attic insulation do I need?

ENERGY STAR recommends R-49 to R-60 for most of the northern US and R-30 to R-60 in warmer areas. Subtract what you have, divide by the product's R per inch, and the insulation calculator converts that into depth.

Can I put new insulation on top of old insulation?

Yes, if the old insulation is dry and not contaminated. Use unfaced insulation for the new layer so you do not create a second vapour barrier, and seal air leaks first.

Do I need rafter baffles?

In a vented attic with soffit vents, yes. Baffles keep insulation from blocking the air path from the soffits to the roof deck, which prevents moisture and ice-dam problems.