Best insulated crawl space vent covers with self-adhesive backing

Short answer: nothing I found is both insulated and self-adhesive — every crawl space vent cover here is a rigid plastic panel that mounts into or over the opening, so you'd add your own foam board and adhesive tape. Here's how they stack up.

Top pick: Recessed Crawl Space Vent Cover – Shallow Depth Encapsulation Seal. Highest rated of the recessed panels and sold at several stores, so you can compare. It seats inside an 8" x 16" opening and seals it flush — the cleanest base for sticking a cut piece of rigid foam to the back.

Also good:

• Crawl Space Door Systems Shallow Recessed 8H x 16W — same idea, cheapest way to try one vent before doing the whole foundation.
• Foundation Vent Covers (2-pack) — for nailing to floor joists or replacing a block; best if your vents aren't recessed.
• ATMOX Internal Mount (5-pack) — mounts from inside the crawl space, good for a whole-house job where you don't want to touch the outside.
• Small Outward Mounted Cover — paintable ABS that sits on the face of the wall; suits painted foundations and easy seasonal removal.

Skip: the 8" x 16" black cover at the high price — same job as the picks above for far more.