To install radiant barrier is to place a low-emissivity foil surface so that it faces an open air space, and then to fix it so it stays in that position for the service life of the roof. In an attic, that usually means stapling foil to the underside of the rafters. In new construction, it more often means draping foil over the framing before the roof deck goes down. Neither method changes the structure of the roof or its waterproofing, and neither replaces bulk insulation. A radiant barrier acts on radiant heat transfer. It is specified on that basis, and on nothing else.
Where the barrier goes
Three positions cover the majority of installations.
Attic, under the rafters. The foil is stapled to the underside of the roof rafters so that the low-emissivity face points down into the attic volume. The air space between the foil and the roof deck is what the surface needs in order to work; the foil is not pressed against the decking, and it is not laid on top of the floor insulation. Retrofit work of this kind is carried out from inside the attic and follows the rafter line, so rafters that are irregular, obstructed by ducts, or partly concealed by a finished ceiling change both the amount of foil required and the time needed to fit it. More detail on this application is set out in our attic and roof barrier notes.
Sarking-style wall and roof wrap during construction. Where a roof or wall is still open, a foil-faced woven or laminated sarking is installed across the framing before the covering goes on. Typical products in this family include "Aluminum Foil Woven Fabric Build Sarking Radiant Barrier Wall Roof Wrap" and "Reflective Woven Foil Blankets Thermal Heat Reflective Radiant Barrier". On roofs, the foil runs over the rafters and under the roof covering; on walls, it runs across the studs or girts as an external wrap. The same air-space rule applies — the foil needs a cavity on the side it faces.
Metal buildings. In steel-framed sheds and warehouses, foil is commonly draped across purlins or girts and held in place with insulation fasteners, wire, or the cladding fixings themselves. The reflective face is oriented toward the interior.
Reflective foil products of this type carry no published thermal-conductivity figure, because they are specified for radiant behaviour rather than for conduction. Aerogel blankets and vacuum insulation panels sit in a different category: VIP product pages publish a vacuum-core conductivity value (lower than 0.003 W/m·K), while aerogel felt pages state “low thermal conductivity” with no numeric value — which is why the two families are not interchangeable in a specification.
Two common methods to install radiant barrier
Stapled to the rafter undersides. This is the usual retrofit approach. Foil is rolled out horizontally across the rafters, positioned with the reflective face down, and stapled through the flanges at each rafter. Adjacent runs are overlapped, and the overlaps are stapled or taped so the foil layer stays continuous. The installer works along the rafter line, keeping the foil taut enough to hold an air space but not so tight that it tears at the fasteners. Perforated foil is used where the assembly needs to allow moisture to move through the material; non-perforated foil is used where the surface faces a vented, dry cavity. Product options in this family are listed under foil insulation materials.
Draped over the rafters before the decking is fixed. This is the new-build sequence. Foil is unrolled across the top of the rafters or purlins, reflective face down, and the roof deck or cladding is fixed through it or over battens. The practical constraints are sequencing — the foil goes down after the framing is complete and before the decking crew arrives — and fastener penetrations, which should follow the fixing pattern of the roof covering being used. The foil must not block the roof's drainage path or its ventilation openings.
Both methods rely on the same principle: a low-emissivity surface facing an air space. Neither depends on a particular brand, and both follow the generic installation practice found in roofing and insulation trade guidance.
What drives the installed cost
Installed cost is driven by four variables, and the material price is only one of them.
Measured area versus net coverage. Material is bought by area, but coverage is reduced by overlaps, seams, and waste around penetrations. A roof with many hips, valleys, dormers, chimneys, or skylights consumes more foil per unit of floor area than a simple gable.
Roof and attic complexity. Cuts, corner returns, and obstructions — ducts, conduit, recessed lights, and framing that interrupts the rafter line — raise the labour share of the total. Work carried out from inside the attic is slower than work carried out from above.
Access. Attic height, roof pitch, distance from the access hatch, whether the space is floored, and ambient temperature all affect how many hours a crew spends in the attic. Multi-storey buildings add material-handling time.
Existing insulation. Where bulk insulation is already present, it usually has to be moved aside and reinstalled without being compressed. That work is not visible in a material quotation, but it is part of the job.
Material class also shifts the number. Published starting prices on the Qiyao store as of 2026-10-11 are from $0.15 for reflective foil listings, from $12.35 per piece for aerogel felt, and from $3.11 per piece for VIP panels. These are list prices for material and do not represent an installed cost.
Checks before you install radiant barrier
Measure the substrate rather than the room. For attic work this means rafter spacing on centre, rafter depth, and the clear space available between the rafter line and the roof deck; for metal buildings it means purlin or girt spacing on centre. Note the direction the runs will take and count penetrations, since both affect the number of rolls and the number of cuts.
Decide between perforated and non-perforated foil according to where moisture is expected to move. Perforated foil is the usual choice where a vapour-bearing air stream may pass from the space below through the material toward a vented cavity; non-perforated foil is used where the surface sits on the exterior side of the assembly and the cavity behind it is drained and ventilated. The choice is a moisture-management decision, not a ranking of performance.
Order samples before committing to a full roll, particularly to confirm the reflective face, the roll width against rafter spacing, and the handling behaviour of the material. Certificates available upon request.
Industry-typical lead times are 15–25 days for standard orders and 25–35 days for custom sizes; confirm at time of order. Samples are available. Our product and specification guide covers roll widths and material options in more detail.
Hangzhou Qiyao New Material Co., Ltd., an insulation materials manufacturer established 2017 in Hangzhou, Zhejiang, China, lists foil, aerogel, vacuum insulation panel and cold chain lines on its Made-in-China store (1622 products on sale; Audited Supplier; Diamond Member Since 2023). For material selection, roll dimensions, and sample requests, contact Judy at +86 0571 8606 2609 or [email protected].