Comparisons
Radiant Barrier vs Attic Insulation
Radiant barriers reflect radiant heat; insulation slows conductive heat. They solve different problems, and one of them only matters in hot, sunny climates.
Updated October 2026 · about 6 min read
How each works
A radiant barrier is a thin reflective foil stapled to the underside of the rafters. It reflects the sun's radiant heat away from the attic, dropping attic air temperature by 10–30°F on a hot afternoon.
Bulk insulation resists conducted heat in both directions and is what your climate zone R-value target refers to. A foil sheet has essentially no R-value on its own.
Where radiant barriers pay
Hot, sunny climates — the southern third of the US — especially where ductwork runs through the attic. Typical cooling savings are 5–12%, with the biggest gains in homes with attic ducts.
In cold northern climates, savings are close to zero and the money is better spent on more R-value and air sealing.
Gear for this job
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Installation notes
Foil must face an air gap to work; laying it directly on top of attic insulation lets dust settle on it and kills the effect within a few years. Staple it to the rafters, keep it clear of soffit vents, and never wrap it around wiring.
The verdict
Get to your climate-zone R-value target first. Then, if you are in a hot climate with a sun-baked roof, add a radiant barrier as a cooling bonus.
Run the numbers
Frequently asked questions
- Does a radiant barrier replace insulation?
- No. It has virtually no R-value and does nothing for winter heat loss. Use it in addition to a full depth of attic insulation.
- How much does a radiant barrier save?
- Typically 5–12% of cooling costs in hot, sunny climates, and near zero in cold climates.
- Should the foil face up or down?
- It must face an open air space. Rafter-mounted barriers face down into the attic; that gap is what makes reflection work.
Insulation gear worth owning
The tools and materials that show up on almost every insulation job.
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