Foil insulation is a category of reflective materials used to manage radiant heat transfer. Unlike bulk insulation, which slows heat conduction through thickness, foil insulation works primarily by reflecting thermal radiation across an air space. It is supplied as foil laminates, woven foil fabrics, foil blankets, and container liners. This page explains how reflective insulation works and where foil insulation is used: windows, roofs, walls, and other applications. The descriptions below are general physical principles rather than product-specific performance claims. For product data, refer to individual product pages and request certificates when needed. Reflective products are often combined with other materials to form a system; the foil layer is one component. Installation details determine whether the reflective surface has an air gap.
How reflective insulation works
Heat moves by conduction, convection, and radiation. Reflective insulation addresses the radiation component. All surfaces emit and absorb thermal radiation according to emissivity. A low-emissivity surface emits less infrared radiation than a high-emissivity surface. Aluminum foil is commonly used in reflective insulation because it has low emissivity in the infrared range. When radiant heat reaches a low-emissivity foil surface, a portion of that energy is reflected rather than absorbed and re-emitted. This reduces radiant heat flow between the foil and the adjacent air space.
Air gaps are essential. A reflective surface must face an air space to reduce radiant transfer. If the foil is in direct contact with another material on both sides, conduction becomes the dominant path and the reflective function is limited. The air space provides a low-conductivity medium and allows radiation to remain a significant mode of heat transfer. The orientation of the air space—horizontal, vertical, or sloped—affects convection within the cavity. Sealing and installation quality also influence performance.
Reflective insulation is not the same as bulk insulation. A foil layer by itself does not provide a thickness-based R-value. System performance depends on the number of air spaces, surface orientation, dust accumulation, and how the materials are installed. Reflective foil products carry no published thermal-conductivity value; they work by reflecting radiant heat. This distinction matters when comparing foil insulation with fiberglass, mineral wool, foam, or aerogel blankets.
In construction, reflective insulation is often part of a layered assembly. A foil facing may be laminated to woven fabric, bubble material, or paper. The foil layer acts as a radiant barrier, while the substrate provides mechanical support or additional functions. Some assemblies combine the foil with other materials to meet mechanical or installation requirements. For material options, see foil insulation products.
Windows and glazing: foil insulation for heat-gain control
Windows are different from opaque building surfaces because they transmit visible light and solar radiation. Foil insulation for windows is generally used as a shading layer rather than as a transparent glazing material. Common forms include roller shades, blinds, removable panels, and foil-faced covers. The reflective surface faces the glass or the room, depending on whether the goal is to reduce solar heat gain or reduce radiant heat loss.
In warm conditions, a reflective shade installed with an air gap between the foil and the glass can reflect a portion of incoming solar radiation before it becomes interior heat. In cool conditions, a low-emissivity surface facing the room can reduce radiant heat loss from occupants and interior surfaces. In both cases, the air gap is critical. If the foil touches the glass, conduction increases and the reflective benefit is reduced.
Foil insulation for windows does not replace double glazing, low-e glass, or insulated frames. It addresses radiant transfer and solar gain. It can also reduce daylight, so it is typically used where privacy, cooling load reduction, or seasonal shading is acceptable. For window applications, the foil should be installed so that the reflective surface remains clean and facing the intended air space.
The same physical principle applies at different scales: a small removable cover for a vehicle window and a large foil shade for a commercial glazing system both rely on reflection and air-space separation. Product-specific data should come from the supplier, because foil products do not carry published thermal-conductivity values.
Roofs and attics: foil insulation as sarking and blankets
Roofs receive solar radiation over a large area. The roof surface heats and radiates energy downward toward the attic or ceiling. A reflective foil installed under the roof cladding can reduce this radiant component when it faces an air space. One product used for this purpose is "Aluminum Foil Woven Fabric Build Sarking Radiant Barrier Wall Roof Wrap". It is a woven foil fabric intended as sarking wrap for roof and wall assemblies.
Sarking wrap is typically installed over rafters or sheathing, beneath the roof covering. The foil surface faces the attic or cavity air space. The assembly should maintain an air gap; if the foil is pressed directly against another material, conductive heat transfer bypasses the reflective surface. In attics, "Reflective Woven Foil Blankets Thermal Heat Reflective Radiant Barrier" are used as reflective blankets. They can be installed with an air space to reflect radiant heat from the hot roof deck.
Attic and roof applications often combine reflective foil with bulk insulation. The bulk insulation reduces conductive and convective heat flow, while the foil addresses radiation across the adjacent air space. The order of layers, the direction of the foil face, and the continuity of the air gap all affect results. Dust on the foil surface can reduce emissivity performance over time. For more on this application, see attic and roof barrier guidance.
Ventilation also matters. A ventilated attic can remove heat that accumulates in the roof assembly, while a reflective barrier reduces the radiant portion entering the attic. Neither measure alone describes the whole thermal performance of a roof. The relevant product data for foil insulation remains the reflective function, not a published thermal-conductivity value.
Walls and other uses: foil insulation in wraps and container liners
Wall assemblies use foil insulation as a facing or wrap. In a wall cavity, the foil can be installed facing an air space, where it reflects radiant heat between the cavity surfaces. The same rule applies: the reflective surface needs an air space to work as a radiant barrier. If the foil is compressed against framing or sheathing, the reflective function is reduced.
Foil laminates are also used in packaging and protective covers. "Reflective Pet Al PE Laminated Foil Pet+Alu+PE" is a PET/aluminum/PE foil laminate (per its product name). In these uses, the foil reflects radiant heat and can reduce heat exchange between the contents and the surrounding environment. Cold chain packaging often combines reflective foil with other insulating materials.
For transport, "40FT Aluminum Foil Thermal Insulated Bag Custom Container Liner" is a container liner that uses foil to create a reflective layer inside a shipping container. The liner reduces radiant heat gain or loss through the container walls and roof, depending on the installation. Similar foil bags and liners are used for pallet covers and reusable transport packaging.
When selecting foil insulation for walls, packaging, or container liners, compare the construction, the number of air spaces, and the installation method. Material comparisons are available in foil insulation comparisons.
Hangzhou Qiyao New Material Co., Ltd., an insulation materials manufacturer established 2017 in Hangzhou, Zhejiang, China, lists reflective foil, aerogel, vacuum insulation panel and cold chain lines on its Made-in-China store. Contact Judy at +86 0571 8606 2609 or [email protected]. OEM/ODM and samples are available. 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. For specific foil insulation uses, share the assembly and air-space details with the supplier.