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Blown-in vs batt insulation: which fits your attic?

Blown-in fills gaps around obstructions; batts must be hand-cut. Compare coverage, R-value per inch, and where each works best in an attic.

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Blown-in vs batt insulation: which fits your attic?

What's the difference between blown-in and batt insulation?

Blown-in is loose fibers packed in by machine; batts are pre-cut blankets you lay between joists or studs. The Department of Energy notes blown-in fills irregular areas and gaps around obstructions, while batts must be hand-cut to fit. In an existing attic floor, blown-in usually gives more consistent coverage with fewer gaps.

What's the difference between blown-in and batt insulation?

Where does each one actually win?

Standard fiberglass batts run about R-3.1 to R-4.3 per inch and a homeowner can install them - their weak spot is fit, since the DOE warns that gaps and compression lower the real R-value. That is why batts shine in open new-construction walls and accessible joist bays, while blown-in tends to win on an existing, obstruction-filled attic floor where consistent coverage matters more than material cost.

Sources

2 cited
  1. Blown-in vs batt coverage and fit: U.S. Department of Energy, Insulation Fact Sheet, DOE/CE-0180, 2008 (checked 2026-08-19).
  2. Fiberglass batt R-value per inch: Colorado Energy, R-Value Table: Common Building Materials (checked 2026-08-19).
How it works

How blown-in insulation is actually installed

Four steps, done in order. The Department of Energy is explicit that skipping the air-sealing step is the most common way a new insulation job still leaves an attic underperforming.

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  1. 1

    Air seal first

    The EPA recommends sealing attic-floor penetrations before insulating, because loose-fill does not stop air moving through gaps around wiring, pipes and fixtures.

  2. 2

    Add baffles and depth markers

    Rafter baffles keep blown material off the eaves where it could get wet, and depth rulers mark the target R-value before the blower starts.

  3. 3

    Blow to depth

    A pneumatic machine feeds loose fiberglass or cellulose over the attic floor, covering the tops of the joists so heat cannot bypass the insulation.

  4. 4

    Verify and clean up

    The settled depth gets checked against the target R-value for your climate zone, then tools and debris are cleared.

How we work

What this site will and will not do

We explain the R-value target and the real cost drivers first, and we do not sell you the installation - which is why we can say plainly when topping up beats a full replacement.

01

R-value before a quote

ENERGY STAR recommends R-30 to R-60 depending on your climate zone. Knowing your target before you call means you can hold every bid to the same number.

02

Air sealing first, always

The Department of Energy is explicit that insulation slows heat flow but does not stop air leaks - sealing gaps first is what makes the insulation you pay for actually perform.

03

We are not the installer

We do not install anything ourselves, so we have nothing to gain from steering you toward the bigger job. Licensed local companies do the work and quote it themselves.

04

Nothing we cannot source

Every figure on this site traces to a named, dated source - HomeAdvisor, the DOE, ENERGY STAR, the EPA or the FTC. Where we have not sourced a number, we say so instead of guessing.

Questions

Frequently asked

The questions people actually type before calling a company.

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

Neither is universally better. Blown-in fills irregular areas and obstructions more consistently on an existing attic floor; batts work well in open, evenly spaced joist bays with clear access.

Why does batt insulation sometimes underperform its rated R-value?

Gaps from imperfect cutting, and compression when a batt is squeezed into a too-thin cavity, both lower the real installed R-value below what the batt is rated for.

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