A radiant barrier spray is a coating applied to a building surface — most often roof decking — to reduce radiant heat transfer. Foil products pursue the same objective with a continuous reflective sheet. The two are frequently compared, and supplier descriptions of both use similar vocabulary: reflectivity, emissivity, heat rejection. This page sets out what each product type is, what published product data does and does not say, and which questions a buyer should ask before treating any performance claim as settled. It does not rank the two options, and it assigns no effectiveness percentage to either. The comparison is written for specifiers, contractors and procurement teams who need to separate measured values from descriptive language. Where a figure is not published, that is stated plainly.
What radiant barrier spray is
A radiant barrier spray is a low-emissivity paint or coating supplied in liquid form and applied on site. Formulations differ between manufacturers, but the common design is a binder carrying aluminium pigment, ceramic particles, or a combination, which is sprayed — sometimes rolled or brushed — onto a substrate and left to cure into a thin bonded film.
The working principle is emissivity. A warm surface radiates heat toward cooler surfaces facing it. Lowering the emissivity of that surface reduces the amount of radiant energy it re-emits. In a roof assembly, the surface in question is usually the underside of the roof decking, and the recipient is the attic or plenum space below it. Spray products are also used on walls, metal building surfaces, and equipment housings, where the same principle applies.
Several variables determine what the finished coating actually does:
- Coverage. How much of the intended surface received coating, including areas behind obstructions.
- Dry film thickness. Set by the number of passes, the application rate, and the solids content of the product.
- Surface preparation and adhesion. Coatings applied over dust, rust, moisture, or incompatible existing finishes may not bond as intended.
- Substrate. Decking material, surface texture, and temperature at the time of application all influence the cured film.
- Time. Film condition changes with age, thermal cycling, and exposure.
Because the reflective layer is created during installation rather than in a factory, its properties depend on the applicator. Spray equipment reaches irregular geometry — trusses, fasteners, pipe penetrations, transitions — where a sheet material would require cutting and fitting. The trade-off is that the finished film is difficult to inspect afterwards; verifying thickness generally requires measurement while the work is in progress.
Published performance data for sprays is usually manufacturer-supplied. Comparisons across products are complicated because the substrates and conditions in each test may differ.
What foil does differently
Radiant foil products are solid sheets rather than applied coatings. The reflective layer is aluminium, either as a foil on its own or laminated to carriers such as PET, PE, woven fabric, or kraft paper. Qiyao's catalogue includes "Reflective Pet Al PE Laminated Foil Pet+Alu+PE", "Aluminum Foil Woven Fabric Build Sarking Radiant Barrier Wall Roof Wrap", and "Reflective Woven Foil Blankets Thermal Heat Reflective Radiant Barrier". Reflective foil products start from $0.15 (starting price listed on the supplier's product pages, 2026-10-11).
The mechanism is reflection at a surface rather than a reduction in emission from a coated substrate. Because the sheet is manufactured, its construction — layer order, laminate, surface finish — is fixed before it reaches the site. What installation determines is whether the reflective surface is positioned to face an air space, remains continuous, and stays clean; a dusty, painted, or fully contact-bonded reflective surface is not functioning as a radiant barrier.
Qiyao also lists insulation products that are often specified alongside foil. Vacuum insulation panels are listed with a vacuum core thermal conductivity lower than 0.003 W/m·K. Silica aerogel blankets and felt are described on their product pages as having low thermal conductivity — no numeric value is published — and include "Aluminum Faced 3mm 6mm 10mm Silica Aerogel Insulation Blanket" and "Low Thermal Conductivity Aerogel Blanket Aerogel Thermal Insulation Felt"; some aerogel items note thickness available in customized options. Reflective foil products themselves carry no published thermal-conductivity value, because they work by reflecting radiant heat rather than by resisting conducted heat through a bulk material.
The distinction between reflective and bulk insulation is treated in more detail in reflective vs bulk insulation.
The evidence question: radiant barrier spray vs foil testing
Effectiveness claims for radiant barrier sprays vary between products, and the variation is not resolved by the language used to describe them. "Reflects heat" and "blocks radiant heat" are descriptions, not measurements. What determines whether a claim is useful is its basis: who measured, on what substrate, at what film thickness or product construction, under what conditions, and by which method.
Buyers should ask any supplier — spray or foil — for the specific test basis behind a performance statement. Useful questions include: what property was measured (emissivity, surface temperature, heat flux, or an assembly-level metric)? Was the test performed on the product alone or within a complete roof or wall assembly? Was it a laboratory test or a field test? Was the sample prepared the way it will exist in service? A supplier that cannot answer these questions is asking the buyer to accept an assertion rather than a result.
"Certificates available upon request" is a reasonable starting point, but a certificate is not a test report. Certificates generally attest to a management system or a listing; test reports show the method, the sample, and the measured outcome. When comparing a radiant barrier spray with a foil product, request the report and check that the sample described resembles the material being purchased — same substrate, same thickness, same construction.
For foil, the corresponding question is whether the reflective surface will stay reflective and stay continuous over the service life of the assembly. For spray, the corresponding question is whether the applied coating achieved the emissivity that the supplier's claim assumes, on the substrate actually present. Neither question can be answered from a product description alone.
As a matter of record: reflective foil products from Qiyao carry no published thermal-conductivity figure; the vacuum core of the VIP range is stated as lower than 0.003 W/m·K; aerogel products are described only as low thermal conductivity. That is the extent of the published values. Where a number does not appear, it should not be assumed.
Installation practice for foil-based assemblies is covered in the radiant barrier installation guide.
Practical differences: radiant barrier spray vs foil
Retrofit ease. Spray reaches surfaces that are already in place and awkward to cover with sheet material, and it can be applied around obstructions without cutting. Foil requires access, measurement, cutting, and fastening, which is slower on complex geometry but produces a serviceable assembly on flat or regular surfaces, including roof sarking and wall wraps.
Coverage uniformity. Spray uniformity depends on the applicator, the equipment, and site conditions. Foil coverage is a function of how sheets are laid, lapped, and sealed; the material is dimensionally uniform as manufactured, but gaps and compression at laps and edges are installation issues.
Durability. Cured spray films can be abraded or damaged by subsequent trade work and by repeated contact, and adhesion depends on preparation. Foil can be torn or punctured during and after installation, and laminates vary in how they behave when creased or folded. The reflective surface fails in both cases the same way — by becoming non-reflective or discontinuous.
Cost structure. Spray cost is dominated by labour: surface preparation, masking, application, and cure time, with material a smaller share. Foil cost is material plus installation labour, and the material side is published — reflective foil from $0.15. Foil is supplied in rolls and blankets, and Qiyao's foil range lists the specific constructions.
Lead time. Samples are available. Industry-typical lead times are 15–25 days for standard orders and 25–35 days for custom sizes; confirm at time of order.
Hangzhou Qiyao New Material Co., Ltd., an insulation materials manufacturer established 2017 in Hangzhou, Zhejiang, China, lists reflective foil, vacuum insulation panels, aerogel blankets and cold chain products on its Made-in-China store (Diamond Member Since 2023; Audited Supplier; 5.0/5 rating; 1622 products on sale). OEM/ODM and samples are available. Certificates available upon request. Contact: Judy, +86 0571 8606 2609, [email protected]. Buyers weighing a radiant barrier spray against foil should request the test basis behind any performance claim before specifying.
META_TITLE: Radiant Barrier Spray vs Foil: What Evidence Shows META_DESC: A technical comparison of radiant barrier spray and reflective foil: mechanisms, published values, and the test questions buyers should ask.