Blog · 2026-11-13
Radiant Barriers: What They Actually Do (and When They Earn Their Keep)
On a July afternoon in Maryland, your roof shingles can pass 160 degrees, and the underside of the roof deck radiates that heat down at your attic floor like a broiler element. Regular insulation slows heat that conducts and convects — but radiant heat travels in a straight line until it hits something. A radiant barrier is that something: a low-emissivity foil surface, stapled to the rafters or laid over the attic floor, that reflects radiant heat instead of absorbing and re-emitting it.
Radiant heat, in plain terms
Hold your hand near a hot stove without touching it and you feel radiant heat. Your attic ceiling feels the same thing from the roof deck all summer. Fiberglass and cellulose absorb that radiation, heat up, and pass the warmth along. Foil mostly refuses the transaction — it reflects the energy back toward the roof, where ventilation carries part of it away. Attic temperatures can drop meaningfully on peak days, ductwork sitting in the attic runs cooler, and the ceiling below stops acting like a warming tray for the rooms under it.
What a radiant barrier is not
It has almost no R-value of its own and it is not a substitute for insulation depth. A foil sheet over four inches of tired fiberglass gives you a cool-running attic that still leaks heat all winter. The products work as partners: depth handles winter and conduction, the barrier handles summer radiation. It also does nothing draped loosely, dust-covered on the floor (dust kills reflectivity over time, which is why rafter installation is the durable choice), or installed without an air gap — foil pressed tight against a surface just conducts.
Where it earns its keep in our climate
Maryland is a mixed climate, so the case is seasonal and specific: homes with ductwork in the attic, west- and south-facing roof planes with no shade, top-floor rooms that overheat while the thermostat downstairs is satisfied, and homeowners whose summer bills sting worse than their winter ones. In those homes, a radiant barrier installation paired with proper attic insulation depth is one of the few upgrades you can feel the same week. In a shaded house with ducts indoors and no summer complaint, we will tell you to spend the money on sealing and depth instead.
How we install it
Perforated foil — never the vapor-trapping solid kind in a vented attic — stapled to the underside of the rafters, kept clear of the soffit vents so the attic still breathes, and stopped short of anything hot. It is a one-day job in most attics and combines naturally with a blown-in top-up scheduled the same visit.
Curious whether your attic is a candidate? The free assessment will tell you, with the roof planes and duct layout photographed. Call Eagle Insulation Services at (855) 640-0404 — answered 24/7.
Want us to look at your attic?
Book a free assessment — depth measured, leaks photographed, options in writing.