The main types of home insulation are fiberglass, as batts or blown-in loose-fill; cellulose, blown loose or dense-packed; mineral wool, often called by the brand name Rockwool; spray foam, open cell or closed cell; and rigid foam board in three plastics, EPS, XPS and polyiso. None is best everywhere. The right one depends on where it goes, whether water can reach it, how much depth the framing allows, and the budget.
Two things matter as much as the product. Fiber insulation doesn’t stop air, so the leaks get sealed first. And the R-value on the label shows up in the house only when the insulation fills the space without gaps or compression.
Types of insulation compared
R-value per inch, and what a 3 1/2-inch bay holds. Federal rules make ads that quote R-values say it plainly: “The higher the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.”
- Fiberglass batts: about R-3.1 to R-4.3 per inch; R-11 to R-15 in a 3 1/2-inch bay. Low cost, not an air barrier.
- Blown fiberglass: about R-2.4 to R-3 per inch in two manufacturers’ attic charts. Light, fills around obstacles, needs the most depth.
- Cellulose: about R-3.2 to R-3.8 per inch; about R-11 to R-13 in 3 1/2 inches. Low cost, heavy, slows air when dense-packed, dislikes water.
- Mineral wool: about R-4 per inch; R-15 in 3 1/2 inches. Noncombustible, water resistant, good for sound.
- Open cell spray foam: R-3.9 to R-4.2 per inch; about R-14 in 3 1/2 inches. Air seals, vapor-open.
- Closed cell spray foam: R-6.9 to R-7.1 per inch; about R-24 in 3 1/2 inches. Air seals, vapor retarder, water resistant.
- EPS board: R-3.6 to R-4.2 per inch, by grade.
- XPS board: R-5 per inch. Moisture resistant.
- Polyiso board: R-6 at 1 inch on one foil-faced sheathing label, less in the cold.
On cost, the Department of Energy’s Building America insulation guide ranks cellulose, fiberglass batts and blown fiberglass lowest, mineral wool batts a step up, foam board higher and spray foam highest.
Fiberglass insulation: batts and blown-in
Fiberglass batts
Batts are blankets of glass fiber cut to stud and joist spacing. One manufacturer’s range: R-13 and R-15 at 3 1/2 inches for 2x4 walls, R-21 at 5 1/2 inches for 2x6 walls, and R-30, R-38 and R-49 at 9 1/2, 12 and 14 inches for attics and floors. Denser batts carry more R-value in the same bay.
They are the cheapest way to fill open, regular framing. The Department of Energy’s guide lists the catches: batts aren’t air-tight, air leaking around their edges significantly reduces R-value, they are hard to fit into irregular spaces, they lose R-value when compressed, and rodents nest in them. One data sheet shows the compression cost: an R-19 batt, 6 1/4 inches thick, delivers R-18 squeezed into a 5 1/2-inch 2x6 wall.
Blown-in fiberglass
Loose-fill fiberglass is blown across attic floors or dense-packed into closed walls. It is light and settles little, but takes depth: two manufacturers’ charts call for 16 3/4 and about 20 1/4 inches for R-49. The Department of Energy warns that many blowing machines over-fluff it, lowering density and R-value, so the bag count matters as much as the depth. See attic insulation.
Cellulose insulation: loose-fill and dense-pack
Cellulose is recycled paper, mostly newsprint, treated with borate, sometimes blended with ammonium sulfate, for fire and insect resistance, according to the Department of Energy. At about R-3.2 to R-3.8 per inch, it packs more R-value into an inch than blown fiberglass.
- Loose-fill goes on open attic floors. It settles, so its coverage chart lists an installed and a settled depth, and the federal R-value rule has it tested at settled density. At R-49 it weighs about two and a half times as much as blown fiberglass in the charts above.
- Dense-pack is blown through holes into closed walls and sloped ceilings at high density. The Department of Energy says cellulose at proper density cannot settle in a cavity, and its guide credits dense-pack with some air sealing ability, if the walls can take the pressure.
The weakness is water. The same guide warns that wetting and high humidity can make cellulose absorb large quantities of water, cutting its thermal resistance, draining the fire retardant and risking mold, and that it must be kept away from chimneys and metal flues.
Mineral wool (Rockwool) insulation
Mineral wool is rock or steel-mill slag, melted and spun into fiber. ROCKWOOL’s Comfortbatt data sheet lists R-15 at 3 1/2 inches, R-23 at 5 1/2, R-30 at 7 1/4 and R-38 at 9 1/2, at a density above 1.8 pounds per cubic foot, and the maker says it cuts easily around pipes, wiring boxes and ducts.
- Fire: noncombustible under ASTM E136, flame spread and smoke-developed indexes of 0.
- Water: the maker calls stone wool water resistant and says it doesn’t rot or promote mold. At 42 perms for 3 1/2 inches it is vapor-open, so it won’t stop moisture reaching a cold surface.
- Sound: the Department of Energy’s guide rates it excellent sound insulation.
Rockwool or fiberglass? In a plain exterior wall, fiberglass does the thermal job for less. Mineral wool earns its price where fire, sound or a tight fit around obstructions matters, as in bedroom walls and floors between stories.
Spray foam: open cell and closed cell
Spray foam air seals as it insulates and fills stone, block and irregular framing. Open cell is soft, vapor-open and cheaper; closed cell is rigid, water resistant and a vapor retarder at about 1 1/2 inches. It costs the most, so it belongs at rim joists, roof decks, foundation walls and shallow rafters, under a code-required thermal barrier such as 1/2-inch drywall in living space. See spray foam insulation and open cell vs closed cell spray foam.
Rigid foam board: EPS, XPS and polyiso
Foam board does a job cavity insulation can’t: a continuous layer over studs, foundations and roof decks that stops heat traveling through the framing. The Department of Energy’s guide notes it is an air barrier and vapor retarder only if its seams are properly sealed. All three types need a thermal barrier indoors.
- EPS, expanded polystyrene: R-3.6 per inch on one maker’s data sheet, R-4.0 and R-4.2 for denser grades in the EPS Industry Alliance’s figures. The Department of Energy calls it the least expensive board and notes it absorbs some water and isn’t a vapor retarder.
- XPS, extruded polystyrene: R-5 per inch at a 75°F mean temperature on Owens Corning’s data sheet, rising to R-5.6 at 25°F, with lab water absorption of 0.3 percent by volume or less. The Department of Energy calls it the preferred board for soil contact.
- Polyiso, polyisocyanurate: one of the highest label R-values, R-6 at 1 inch on Johns Manville’s foil-faced sheathing, whose foil makes it a Class I vapor retarder. Cold is its weakness: Building Science Corporation found its R-value drops as outdoor temperatures fall below freezing, and reports that the National Roofing Contractors Association designs with R-5.0 per inch in cold climates. The Department of Energy says to keep it out of contact with soil.
EPS and XPS gain R-value as they get colder; polyiso loses it. Outside a wall in a Northeast winter, that can outweigh the label.
Which insulation goes where
- Vented attic floor: blown cellulose or fiberglass over air sealing, or unfaced batts in open, regular bays.
- Roof deck, unvented attic or cathedral ceiling: closed cell foam, open cell with the vapor retarder coating the code requires in zone 5 and colder, or foam board on the deck at a reroof.
- Open exterior walls: fiberglass or mineral wool batts, or spray foam, with foam board outside where the energy code calls for continuous insulation.
- Closed exterior walls: dense-pack cellulose or blown fiberglass through holes; standard spray foam can’t go into a finished wall. See wall insulation.
- Rim joists: closed cell foam, or board cut to each bay and sealed at the edges.
- Basement walls: closed cell foam or foam board against the concrete, never fiberglass or cellulose; batts only in a stud wall in front of the foam. See basement insulation.
- Crawl spaces: closed cell or board on the walls of a sealed crawl space; batts or closed cell in the floor above a vented one. See crawl space insulation.
- Floors over garages and unheated basements: batts held tight to the subfloor, or closed cell foam. See garage insulation.
- Slab edges: XPS, not polyiso.
- Interior walls and floors for sound: mineral wool or fiberglass batts.
- Under new siding: foam board. ENERGY STAR recommends adding R-5 to R-10 of it in climate zones 4 through 8 whenever siding comes off.
Air sealing, moisture, fire, sound and pests
Air sealing
Spray foam air seals, foam board does when every seam is sealed, and dense-pack cellulose slows air. Batts and loose-fill don’t: the energy code says air-permeable insulation shall not be used as a sealing material. See air sealing.
Moisture
Closed cell foam and XPS resist water, EPS absorbs some, and mineral wool’s maker calls it water resistant. The Department of Energy says fiberglass batts and cellulose hold water and keeps both off basement and crawl space walls. Wet insulation is a symptom; fix the water first.
Fire
Mineral wool is noncombustible. The Department of Energy notes fiberglass itself is noncombustible but its resin binders burn, and one maker’s data sheet says kraft and standard foil facings burn and can’t be left exposed. Cellulose is treated with fire retardant and must meet the Consumer Product Safety Commission’s rules (16 CFR Parts 1209 and 1404, under IRC Section R302.10.3), though the Department of Energy says it can smolder if hot enough. Spray foam and foam board are combustible and need a thermal barrier indoors (Section R316.4 of the 2021 IRC, R303.4 of the 2024 IRC). Mineral wool and glass fiber batts are on the residential code’s list of fireblocking materials (Section R302.11.1).
Sound
The Department of Energy’s guide rates mineral wool excellent for sound, and a Building America guide lists a 2x4 wall filled with open cell foam at STC 37. Cavity insulation helps with voices and television; footsteps travel through the framing. See basement ceiling insulation.
Pests
No insulation keeps mice out. The Department of Energy lists batts as nesting material for rodents, and cellulose’s borate is for insects. The CDC says a mouse fits through a hole the width of a pencil, 1/4 inch, and advises steel wool held with caulk or spray foam for small holes and metal, cement or hardware cloth for larger ones. Insulation soiled by rodents comes out before anything new goes in.
Recycled content
By the Department of Energy’s figures, cellulose is 82 to 85 percent recycled paper, mineral wool averages 75 percent post-industrial recycled content, and most fiberglass makers use up to 40 to 60 percent recycled glass.
Faced or unfaced insulation
A facing is kraft paper or foil on one side of a batt. It makes the batt a vapor retarder: the residential code rates kraft-faced batts Class II, and one maker lists kraft at 1.0 perm and foil at 0.5. Both burn, so a facing belongs against the finish, never exposed.
- Exterior walls: facing toward the heated room. In climate zones 5 and 6, which take in seven New Jersey counties, all of Connecticut and the Hudson Valley counties outside Westchester, the code wants a Class I or II vapor retarder on the room side, with exceptions for vented siding and exterior foam, and kraft-faced batts meet it. In zone 4, the rest of New Jersey, Westchester and Long Island, polyethylene sheeting isn’t permitted on the room side, and kraft or ordinary latex paint meets the code (IRC Section R702.7).
- Attic floors: Building America recommends unfaced batts in zone 4 and faced batts, paper down, in zones 5 and 6. Over existing insulation, unfaced only.
- Floors over crawl spaces, garages and unheated basements: unfaced works; if faced, the paper goes up, against the subfloor.
- Basement walls: unfaced batts in a stud wall in front of foam. The code exempts basement walls from its vapor retarder rule, and plastic or foil on the room side keeps the wall from drying.
- Left exposed: the Department of Energy notes batts with a flame-resistant facing are made for basement walls that stay uncovered.
- Interior sound walls: unfaced.
Why installed insulation falls short of its label
Under the Federal Trade Commission’s R-value Rule, the number on the bag is measured in a lab on the insulation alone at a 75°F mean temperature, and every fact sheet must warn: “To get the marked R-value, it is essential that this insulation be installed properly.” In a house, four things pull it down.
- Gaps. The Department of Energy’s Building America guide says even small gaps add up to a large reduction in effective R-value, like holes in a blanket, and its Solution Center warns that gaps and compressions leave cold spots where condensation can form. The Building America guide adds that batts must not be folded, tucked in or pinched, and should be slit around wiring and plumbing.
- Compression. Compressed insulation will not provide its full rated R-value, the Department of Energy says: a batt crushed behind a cable, or loose-fill flattened by stored boxes.
- Framing. Studs and headers conduct heat around the insulation. Oak Ridge National Laboratory modeled a 2x6 wall with R-19 batts, studs 24 inches apart, at R-16.4 through its clear section and R-13.7 for the whole wall with its corners and connections. Continuous board over the studs is the fix.
- Air, temperature, age and moisture. Air moving through fiber carries heat past it, and the Department of Energy notes most insulation’s R-value also depends on temperature, aging and moisture.
The same federal rule protects the buyer. An installer’s receipt must show the coverage area, thickness and R-value installed, and for loose-fill the installed and settled thickness and number of bags. If a quote specifies a depth of insulation and never mentions air sealing, it is half a job.
Signs your insulation isn’t working
ENERGY STAR ties these complaints to insulation and air leaks: drafty rooms, rooms hotter or colder than the rest of the house, high heating and cooling bills, ice dams, cold floors in winter, and pests. What to check:
- Attic depth. If the insulation is level with or below the tops of the joists, ENERGY STAR says you probably need more; thin spots at the eaves count. To estimate what is there, it multiplies the depth in inches by about 2.5 for loose fiberglass, 2.8 for rock wool, 3.7 for cellulose and 3.2 for fiberglass batts.
- Dirty or frosty insulation. Dark patches are house dust filtered out of air leaking through, ENERGY STAR explains; frost or water stains mean moist air is reaching the attic.
- Walls. Turn off power to an outlet on an exterior wall, confirm it with a voltage tester, remove the cover and shine a flashlight beside the box. ENERGY STAR says to check every floor, and old and new parts of the house.
- Basements and crawl spaces. Sagging, fallen or wet batts, or insulation soiled by mice.
- Vermiculite, a pebble-like fill, usually gray-brown or silver-gold. The EPA says to assume it may contain asbestos and leave it undisturbed; work that would disturb it goes to a professional asbestos contractor.
A blower door test finds what a flashlight can’t; see what an energy audit is.
What insulation costs
Most of our projects run between $3,500 and $12,500. A job moves with the material (blown fiber and batts cost far less than spray foam, mineral wool more than fiberglass), the area and target R-value, access, the air sealing, and any fire barrier over foam. Removing wet, settled or rodent-soiled insulation is a line item in our price, done with containment and a HEPA insulation vacuum; mold remediation goes to a remediation company.
The Department of Energy tells homeowners not to be surprised if quotes for the same R-value vary by more than a factor of two, and to ask what air sealing is included. Rebates exist through state and utility programs; see New York and New Jersey insulation rebates and Connecticut insulation rebates. The federal 25C tax credit ended for anything placed in service after 31 December 2025. Foam pricing: spray foam insulation cost.
Common questions about types of insulation
What are the different types of insulation?
Fiberglass, as batts or blown loose-fill; cellulose, blown loose or dense-packed; mineral wool batts; open cell and closed cell spray foam; and rigid foam board in EPS, XPS and polyiso. Radiant barriers are sold alongside them, but the Department of Energy notes a radiant barrier has no inherent R-value.
What is the best type of insulation for a house?
Usually several. Blown cellulose or fiberglass on a vented attic floor, closed cell foam at rim joists and on foundation walls, batts or foam in open walls, dense-pack in closed walls, and XPS at slab edges. Whatever the material, the air leaks get sealed first.
Is cellulose or fiberglass insulation better?
In a closed wall, dense-pack cellulose, which slows air and doesn’t settle at proper density. On an attic floor, either: cellulose gets more R-value per inch but is heavy and settles; blown fiberglass is light and settles little but needs more depth. Cellulose handles water worse.
Is mineral wool better than fiberglass insulation?
Not for thermal value alone: a 2x4 bay holds R-15 of either, and fiberglass costs less. Mineral wool is better where fire, sound or a snug fit matters. ROCKWOOL lists its batts as noncombustible with a flame spread index of 0, and the Department of Energy rates mineral wool excellent for sound.
Is spray foam better than fiberglass or cellulose?
It does more per inch and air seals as it goes, but costs the most. It pays at rim joists, roof decks, foundation walls and shallow rafters. On an open attic floor or in a closed wall, air sealing plus blown cellulose or fiberglass does the job for far less.
Should insulation be faced or unfaced?
It depends on the spot. Faced, paper toward the heated room, in exterior walls in climate zones 5 and 6. Unfaced over existing attic insulation, in basement stud walls and in interior walls. Under floors either, with any facing up against the subfloor. Never leave kraft exposed.
What happens if insulation gets wet?
It insulates poorly until it dries and holds water against wood. The Department of Energy warns wet cellulose loses thermal resistance, drains fire retardant and risks mold. Closed cell foam and XPS resist water. Fix the source first, and replace insulation that stayed wet or grew mold.
Is insulation flammable?
Mineral wool is noncombustible. Fiberglass is too, but its binders burn, and kraft or foil facings burn. Cellulose is treated with fire retardant and must meet federal flammability rules, but can smolder. Spray foam and foam board are combustible and need a thermal barrier, such as 1/2-inch drywall, in living space.
Can you put cellulose on top of fiberglass insulation?
Yes. ENERGY STAR says loose-fill can go over fiberglass batts and batts over loose-fill, as long as batts on top are unfaced. The Department of Energy cautions that a dense material on a light, easily compressed one can lower its R-value. Air seal underneath first.
How much does insulation cost?
Most of our projects run between $3,500 and $12,500. The price follows the material, area, target R-value, access, air sealing and any fire barrier; blown fiber costs the least and spray foam the most.
Choosing insulation for your house
We look at each space before we name a material: what is there now, the air leaks, any sign of water or pests, the framing depth, and how the space is used. Then a written scope: which insulation goes where, how thick, what gets sealed first, and the price. We install every material above, so the advice isn’t tied to one product. The energy audit is free.
Call 914-825-6824 or use the contact form, 8am–8pm, seven days. The Home Insulators is family-owned, based in New Rochelle, NY since 2015, with a 100-plus-person in-house crew that never subcontracts. We work across all of New Jersey, all of Connecticut, New York’s Hudson Valley including Westchester, and Long Island; see our service area.