Honest comparison
Batt vs Blown-In Insulation
Blown-in wins in open attics because it fills what batts bridge; batts win in open walls and anywhere you need the insulation to stay put and be lift-able.
The R-value on the bag is not the fight. Installed the way each product actually installs, the same nominal R performs differently — and the difference is gaps. An attic floor is a minefield of joists, wiring, pipes, junction boxes and odd bays. Batts are rectangles; attics are not. Every place a rectangle meets a non-rectangle either gets hand-cut precisely or becomes a void, and voids are disproportionate: a few percent of missed area costs far more than a few percent of performance, because heat takes the bypass.
Loose fill is the opposite trade. Blown as a fluffy monolith, it flows around every obstruction and fills every bay to one continuous depth — coverage is its superpower. Its weaknesses are mechanical: it settles over the years (the bag's stated settled thickness is the honest number, not the fresh-blown fluff), it cannot hold itself in a vertical open wall, and once it is down, working in that attic means swimming in it.
The machine is the practical pivot. Blowing needs a hopper and a hose — rentable, loud, a two-person job for an afternoon. Batts need a knife and patience. For one small area, batts win on logistics alone; for a whole open attic, the machine pays for itself in coverage quality.
The factors that actually differ
| Batts (rolls) | Blown-in (loose fill) | |
|---|---|---|
| Gap performance | Only as good as the cutting; every service penetration is a hand-fitted joint. | Flows around obstructions; continuous coverage is the default, not the achievement. |
| Where it can go | Anywhere it can be held: walls, sloped ceilings, floors, between exposed studs. | Horizontal or contained cavities only; an open vertical wall will not hold it. |
| Settling | Holds its loft if not compressed at install. | Settles by design — depth must be blown to the chart's initial thickness to end at the rated settled R. |
| Future access | Lift a batt, do the wiring, lay it back. | Every later job in the attic disturbs the blanket and needs raking back level. |
| Tools | Knife, straightedge, PPE. | Blowing machine (usually free-with-purchase or rented) plus a feeder at the hopper. |
| Top-ups | Awkward over existing irregular fill. | The natural top-up: blow more over whatever is there. |
Choose batts (rolls) when…
- Open stud walls or rafter slopes — loose fill simply cannot serve them.
- You will need to get back into this attic and want the insulation liftable.
- The area is small enough that machine logistics outweigh coverage gains.
Choose blown-in (loose fill) when…
- A big open attic floor with the usual obstruction chaos.
- Topping up old, uneven existing insulation.
- Coverage quality matters more than future serviceability.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes:
Frequently asked questions
- Is the R-value per inch different?
- Modestly, and it varies more by product than by format. What differs decisively is INSTALLED performance: field studies consistently show gap-related losses dominating product differences. A perfectly cut batt job matches the chart; an ordinary one does not, and loose fill's ordinary job is much closer to its chart.
- Can I blow over old batts?
- Yes — it is the standard top-up and one of blown fill's best uses. The loose fill fills the gaps between and above the old batts. Do not do it the other way round: batts laid over loose fill compress it unevenly and bridge on the high spots.
- What about vents and downlights?
- The same rules for both: baffles keep the eave ventilation path open before any insulation goes near it, and non-rated downlights need clearance or covers. Loose fill makes these details MORE important, because it will happily flow into places batts would never reach — including over the vents.