An attic is the classic radiant-barrier application. On a sunny day the roof deck absorbs solar radiation, rises well above ambient air temperature, and then radiates that energy downward into the attic and eventually into the rooms below. Attic foil interrupts that exchange: a low-emissivity aluminum surface facing the attic reflects radiant heat back toward the deck instead of absorbing and re-emitting it downward. The principle is old, inexpensive, and easy to state. What varies is the format of the foil, where it is placed, and whether the air space it needs survives installation and years of dust. This page covers those variables and the payback logic that follows from them.
Why attics
A pitched roof over a vented attic creates a large, hot, downward-facing surface. Solar radiation heats the roof deck; because the deck has thermal mass, its surface temperature rises above the temperature of the attic air and the surfaces beneath it. Any two surfaces at different temperatures exchange heat by radiation, and the warmer surface — the deck — is the net emitter.
Downward radiation from the deck is what an attic radiant barrier is positioned to intercept. Foil stapled to the sides of the rafters, reflective face down, presents a low-emissivity aluminum surface to the attic. A low-emissivity surface emits little radiation, so much of the energy reaching it is reflected back toward the deck rather than absorbed and re-radiated down to insulation, ducts, and ceiling drywall.
Two limits are worth stating plainly. First, reflective foil products carry no published thermal-conductivity value, because they do not work by resisting conductive heat flow; they work by reflecting radiant heat. Products that resist conduction are specified differently: vacuum core thermal conductivity is listed as lower than 0.003 W/m·K, and aerogel felt as having low thermal conductivity, with no numeric value published. Second, a radiant barrier does not stop conduction through framing or convection through air leaks. Ventilation, air sealing, and bulk insulation remain the primary measures; foil addresses one of the three heat-transfer paths.
In retrofits the barrier is usually installed from inside the attic, stapled across or between rafters. In new construction it can be built into the roof assembly. In both cases one question decides whether it does anything: is there an air space facing the foil?
Which attic foil formats suit a roof deck
Three material families cover most attic work. They differ in how they are installed rather than in the physics.
Woven foil blankets. "Reflective Woven Foil Blankets Thermal Heat Reflective Radiant Barrier" is foil laminated to a woven fabric. The fabric gives the sheet tear and puncture resistance, so it tolerates being stapled across rafter faces and being handled in a confined attic. It is also used as a blanket layer in some roof and wall build-ups.
Sarking wrap. "Aluminum Foil Woven Fabric Build Sarking Radiant Barrier Wall Roof Wrap" is the format for new roofs, installed while the roof is open, across the roof structure before the final covering. Its advantage is timing: the labor of installing it is absorbed into the roofing job.
Laminated film. "Reflective Pet Al PE Laminated Foil Pet+Alu+PE" is a PET/aluminum/PE laminate (per its product name), used as a facing or liner inside composite constructions.
Perforated and solid foils behave differently in moisture terms. Perforated foil lets vapor diffuse through small openings, which reduces the risk of trapping moisture in an assembly that needs to dry inward. Solid foil has low permeance and acts as a vapor retarder — desirable in some assemblies, risky in others. The correct choice follows the drying direction of the specific roof assembly, not a general preference.
Reflective foil carries the lowest listed starting price in the range: from $0.15, with 161 reflective foil insulation products on sale on the Made-in-China store as of 2026-10-11. Where an air space cannot be maintained at all, a reflective product is the wrong tool and a conductive insulant is specified instead — for example "Aluminum Faced 3mm 6mm 10mm Silica Aerogel Insulation Blanket," ; some aerogel products note “thickness available in customized options”. A full list of foil constructions is the better starting point when comparing formats.
Placement rules that matter
The reflective surface must face an air space. That is the whole mechanism. Where foil is pressed flat against decking, battens, or insulation on both sides, heat crosses by conduction and the low-emissivity surface contributes little. In a hot-climate retrofit the usual position is the underside of the rafters, reflective face down into the attic, with the gap maintained across the bays.
Placement also determines whether the foil acts as a vapor retarder or becomes a moisture problem. A low-permeance foil on the warm side of an assembly can trap moisture; a perforated product or a different position avoids it. This is assembly-specific, and the radiant barrier installation guide covers the general sequencing.
Dust is the slow failure mode. A reflective surface works because it is reflective; dust settling on it raises its emissivity and reduces the share of radiant heat it sends back. Surfaces left exposed in an attic collect dust over years, so performance in service is lower than performance at handover. Surfaces that are covered or vertical collect less.
Payback logic follows from the same reasoning. A radiant barrier is a low-cost material layer, but its benefit depends on how much of the attic heat load is actually radiant at the deck, on climate, on existing insulation and air leakage, and on whether it is installed during construction or retrofitted. Installation during a roofing job or a panel build is the case where the incremental cost is mostly material — and the case where the payback arithmetic is easiest to justify.
Sizing an attic foil order
Sizing starts with the roof, not the roll. Measure rafter bay width between rafter faces and bay length, count the bays, then subtract openings and add an allowance for overlaps at hips, valleys, gable ends, and penetrations. Note where a run must change direction, because roll width and run direction decide how much offcut the job produces. Sarking wrap is sized to the roof plane; blankets are sized to the bays they span.
Samples are available for format and handling checks before a full order, and OEM/ODM is available; confirm non-standard options per product. Industry-typical lead times are 15–25 days for standard orders and 25–35 days for custom sizes; confirm at time of order. Certificates available upon request.
Closing note
Radiant barriers are a small part of an attic assembly and a well-defined one: reflective surface, air space, clean face, appropriate permeance. Hangzhou Qiyao New Material Co., Ltd., an insulation materials manufacturer established 2017 in Hangzhou, Zhejiang, China, lists reflective foil, aerogel blankets and vacuum insulation panels on its Made-in-China store; contact Judy at +86 0571 8606 2609 or [email protected]. Application notes by roof and wall type are collected under applications.