The short answer
Blown-in insulation is the right pick for most attics. It costs less. It covers the whole floor evenly. It does the job.
Spray foam is the right pick for tricky attics. It seals air leaks and insulates in one step. It costs more. For some homes it is worth it.
That is the whole comparison in four sentences. The rest of this guide is the detail.
What blown-in does well
Blown-in covers large, open attics fast. A crew can fill a whole attic in hours. The material flows around wires, pipes, and odd corners. The finished blanket is even edge to edge.
It is also easy to top up later. If it settles, we add more. If you remodel, we work around it. It is the flexible choice.
What spray foam does well
Foam seals as it insulates. Every gap it touches closes. In an old, leaky attic that is a big deal. It also sticks where blown-in cannot go: sloped ceilings, tight bays, rim joists.
Foam does not settle or sag. Once it cures, it stays. It also adds some strength to the surface it covers.
The cost difference
We do not post prices, but here is the honest shape of it. Spray foam costs several times more than blown-in for the same attic. The gap is real.
That is why we start most clients with blown-in plus air sealing. That combo gets you most of foam's benefit at a fraction of the price. We suggest foam when the attic truly needs what only foam does.
When we recommend each
Blown-in: open attics, top-ups, budget-conscious jobs, homes that just need depth.
Spray foam: bonus rooms, sloped ceilings, very leaky old attics, attics with ducts on the roof deck.
The trap to avoid
Some companies sell foam for every attic. It is their highest-margin product. Ask what blown-in plus air sealing would do first. If they cannot answer, get a second quote.
Call (301) 679-9193 for a free attic inspection.