Is the R-value of 15.32 realistic?

Only with a clean, sealed air space on the reflective side, which is how the figure is tested. In a typical garage door or attic install, expect a fraction of that, closer to the foam's own small R-value plus a modest radiant gain.

Can I use it alone instead of fiberglass batts?

In mild climates and for radiant heat control on garage doors, sheds and metal buildings, yes. In cold climates or conditioned living space, it works as a radiant barrier and vapor retarder over or under bulk insulation, not as a replacement.

How much area does one roll cover?

A 24 in x 50 ft roll covers 100 sq ft. A standard single garage door is roughly 7 ft by 8 ft, so one roll covers it with some trimming waste.

Does it need an air gap to work?

Yes. The reflective foil needs an air space facing it, typically at least 3/4 inch, to block radiant heat. Foil pressed flat against a surface loses most of its radiant benefit.

How do I seal the seams?

Use a foil-facing tape or a compatible seam tape rated for the foil, and overlap edges by an inch or two. Standard duct tape dries out and lets go over time.

The only new price listed is $26.96 at Walmart as of November 4, 2026. Roll insulation of this type tends to dip in fall and winter, outside the spring and summer building season.