The four insulation types most homeowners choose between are fiberglass batts, blown fiberglass, blown cellulose, and spray foam. Batts work best in open, accessible bays; blown-in fills attics; spray foam wins where space is tight and air-sealing matters most.

Each one trades off R-value per inch, cost, and how it's installed. Pick the wrong type for the space and you'll fight it the whole way. Pick right and the job goes fast. Match your choice to your target with the insulation calculator, and if you need a refresher on the numbers, see R-value explained.

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Fiberglass batts

Batts are the pink (or yellow, or white) rolls and pre-cut panels you picture when you think "insulation." They deliver about R-3.1 to R-3.4 per inch (plan on roughly R-3).

  • Best for: open, accessible stud and joist bays in walls, floors, and new construction
  • Pros: cheap, widely available, easy to handle, no special tools
  • Cons: must be cut carefully around obstructions; gaps and compression kill performance

Batts shine when you can lay them into an open cavity and fluff them to fill it edge to edge. A 2x4 wall takes an R-13 to R-15 batt; a 2x6 wall takes R-19 to R-21. For an attic, R-38 fiberglass batts are an option, but most people get a more even, gap-free result with blown-in up top.

Blown fiberglass

Blown (loose-fill) fiberglass is the same material chopped into fluff and blown through a hose. It runs about R-2.5 per inch, lower than batts because it settles loosely.

  • Best for: attics, and topping up existing insulation
  • Pros: flows into corners and around obstructions; fast over large areas with a rented blower
  • Cons: lower R per inch, so you need more depth; can drift in high wind if soffit baffles are missing

Because it pours into every nook, blown fiberglass beats batts for full, even attic coverage with fewer gaps around joists and wiring.

Blown cellulose

Cellulose is recycled paper treated for fire and pest resistance, blown in like loose-fill fiberglass. It's denser, at about R-3.5 per inch, the highest of the loose-fill options.

  • Best for: attics, and dense-packing existing wall cavities
  • Pros: highest R per inch of the blown materials; good at slowing air movement; recycled content
  • Cons: heavier, settles over time, absorbs moisture if it gets wet

Cellulose hits your target attic depth in fewer inches than blown fiberglass, which is handy when headroom or budget is tight.

Spray foam

Closed-cell spray foam is the heavyweight, delivering about R-6 to R-7 per inch, more than double the loose-fill options. It also air-seals as it expands, doing two jobs at once.

  • Best for: tight spaces, rim joists, irregular cavities, and anywhere air-sealing is critical
  • Pros: highest R per inch; seals air leaks; rigid and structural
  • Cons: most expensive; tricky to install well; over-expansion and waste are easy mistakes

For small jobs like sealing rim joists and gaps, a spray foam gun kit gives far better control than the throwaway straw cans. Big whole-house foam jobs are usually a pro's territory.

Putting it side by side

Here's the quick mental model:

  1. Open wall or floor bay you can reach? Fiberglass batts.
  2. Attic floor, new or topping up? Blown cellulose or blown fiberglass.
  3. Tight space, rim joist, or you need air-sealing too? Closed-cell spray foam.
  4. Want the most R in the fewest inches? Spray foam, then cellulose.

Remember that R-value is additive, so you can mix methods: spray-foam the rim joists for the seal, then blow cellulose across the open attic floor for cheap depth.

Measure twice. Buy once.

The rules that apply to all four

  • Don't compress any of them. Loft is what insulates. A crushed batt loses R-value fast, and packing loose-fill too tight defeats the point.
  • Air-seal before you insulate. Caulk and foam gaps and penetrations first; insulation doesn't stop air leaks on its own.
  • Check the bag's coverage chart. Settled depth and R-value per bag vary by product, so trust the label over any rule of thumb.

The bottom line

Batts for open bays, blown-in for attics and top-ups, spray foam for tight spaces and air-sealing. Fiberglass is cheapest, cellulose packs more R per inch, and foam packs the most while sealing as it goes. Decide your target, pick the type that fits the space, and let the insulation calculator tell you how much to buy.