Insulation comparisons

Spray foam vs blown-in. The honest framing is that these solve overlapping but different problems. Blown cellulose or fiberglass buys you R-value cheaply. Spray foam buys you R-value plus air sealing plus, in the closed-cell case, vapor control - and charges for all three. In an open attic you can just add more depth of cheap material and get the same R for less. In a 3.5-inch cavity you cannot.

Open cell vs closed cell. About R-3.8 per inch versus about R-7, and $0.44-$0.65 versus $1.00-$1.50 per board foot in material, per Fixr. Closed cell is rigid, water-resistant and acts as a vapor retarder at sufficient thickness. Open cell is softer, cheaper, and vapor-open, which some assemblies need in order to dry. "Better" depends entirely on the assembly, and any contractor who says closed cell is always better is not thinking about drying.

DIY vs pro. Air sealing with caulk and canned foam, adding unfaced batts over an accessible attic floor, and insulating a rim joist are genuinely reasonable DIY jobs. Renting a blower for attic loose-fill is doable but works far better with two people. Two-part spray foam is not a DIY job. Isocyanates cause occupational asthma and irritation of the eyes, nose, throat and skin per OSHA, applicators need supplied-air or appropriate respiratory protection, and a bad application can cost $1.50-$3.00 per sq ft to remove - more than you saved.

One thing that changes the math: attic work in a house with knob-and-tube wiring, active roof leaks, or recessed lights that are not IC-rated is not a DIY project regardless of the material. Burying a non-IC fixture in insulation is a fire risk. Fix or box those out first.

How to choose

Pick by assembly, not by product

Open attic floor - cheap blown material. Rim joist and cathedral roof - closed cell. Vented wall that needs to dry - open cell or dense-pack cellulose.

Do not let one bid quote foam and another quote cellulose

Ask every contractor to price the same specified material and R-value. Then, separately, ask what they would do differently and why.

DIY the air sealing even if you hire out the insulation

Caulking top plates, sealing around chimneys and plumbing stacks, and gasketing attic hatches are cheap, high-return, and easy to verify.

Never DIY two-part spray foam

Chemical exposure, mix-ratio control and re-occupancy requirements make this a professional job. A failed application is one of the most expensive mistakes available to a homeowner.

Price the comparison over the same square footage

Whole-house foam averages around $20,000 per Fixr, versus roughly $4,700 for a 2,000 sq ft home insulated conventionally. That gap needs a specific reason to justify it.