Best self-adhesive insulation sheets for crawl space vents

Top pick: Insul-EZ 4ft x 4ft foam sheet with adhesive backing. It's the only one here that's genuinely peel-and-stick, so you can cut a piece to the vent opening, stick it over the grille and pull it off in spring without tools. At 3/4 in and R-3 it's modest insulation, but for stopping cold air through a foundation vent that's usually enough.

Who the others suit:

• Armacell AP self-adhesive sheet — thicker (1 in, R-4.2) and a bigger 36x48 sheet, for colder climates or vents you want to seal harder.
• Owens Corning FOAMULAR boards — the durable choice if you'd rather cut rigid board and tape or glue it in place; they hold up to damp ground contact far better than foam sheets, but you supply the adhesive.
• Reflective foil sheets — best for blocking radiant heat in a hot climate, not for sealing a vent against cold air.

Whichever you use, cut it slightly oversize, seal the edges with foil tape, and leave a few vents open or use vent covers you can open — a crawl space still needs some air movement.