Perforated radiant barrier has thousands of pinholes that let water vapour through. Non-perforated, or solid, does not. Choosing wrongly does not cost you energy performance, it costs you a wet roof, so this is the one specification worth getting right before you order.
The rule
| Situation | Use | Why |
|---|---|---|
| Stapled under rafters, vented attic | Perforated | Vapour reaching the roof assembly must be able to escape |
| Laid over attic floor insulation | Perforated | Solid foil traps house vapour in the insulation below |
| Under a new roof deck, ventilated assembly | Perforated | Same reason, and most codes expect it |
| Wall or crawlspace vapour retarder | Solid | Here you actively want to stop vapour, and the foil doubles as the retarder |
| Behind ductwork or water heater wrap | Solid | No moisture drive to manage |
For attic radiant barrier, which is what almost everyone reading this is doing: perforated.
What goes wrong with solid foil in an attic
Warm indoor air carries water vapour, and it moves upward. In winter that vapour reaches the cold underside of your roof. In a normal vented attic it passes through and leaves via the ridge vent. Put a solid, vapour-impermeable sheet in its path and it condenses instead, on the cold side of the foil or in the insulation beneath it.
The result is damp sheathing, damp insulation, and in a bad case rot in the rafters. It develops slowly and out of sight, which is what makes it worth avoiding by specification rather than by inspection.
Does perforation hurt performance?
Very little. The holes are small and represent a tiny fraction of total surface area, so the reflective surface is essentially intact. Manufacturers publish emittance for perforated products in the same 0.03 to 0.05 band as solid. You are trading a negligible amount of reflectivity for vapour permeability, and it is a good trade in any vented attic.
How to tell what you are buying
Product listings are inconsistent about this, and "breathable" is used loosely. Look for the word perforated in the specification, a stated perm rating (typically above 5 perms for perforated products), or visible pinholes in the product photograph. If a listing does not say, assume solid.
| Product | Price | Rating |
|---|---|---|
| Reflectix radiant barrier, 4 ft x 250 ft perforated (1,000 sq ft) | $148.88 | no ratings yet |
| Radiant barrier perforated aluminium, truss/rafter roll | $158.27 | no ratings yet |
| SmartFOIL double-sided perforated, reinforced | $87.95 | no ratings yet |
| VEVOR double reflective perforated woven roll | $69.90 | 4.5★ (2) |
Live Walmart prices checked 2026-08-29. Prices move; confirm before you buy. We earn a commission on some retailer links, which does not change what we show or what we say about it.
Of the rolls we found, the ones above state perforation explicitly. The RadiantGUARD Xtreme listing does not, so confirm with the seller before buying it for an attic.
Price your own attic in 30 seconds → Free, no account for your first estimate.
See also staple-up vs. deck-applied and the complete radiant barrier guide.