Reflective foil insulation (radiant barrier) works on a different principle from bulk insulation: instead of resisting conductive heat, it reflects radiant heat. A polished aluminium foil surface reflects up to 95–97% of radiant heat and emits very little (low emissivity ~0.03). This makes it highly effective at blocking the intense radiant heat from the sun on Indian roofs — especially when combined with an air gap. It is typically a thin, light, multi-layer product (foil + bubble / foam / woven core).
Reflective foil insulation follows ASTM C1224 (Reflective Insulation). Major brands: Supreme, Aerolam, Insulnergy, U-Tech, Reflectix, LERAFLEX, Cosmofil.
Heat transfers three ways: conduction, convection, radiation. On a hot roof, the sun's heat is mostly radiant. Bulk insulation (wool / foam) resists conduction; reflective foil tackles radiation:
| Type | Construction | Use |
|---|---|---|
| Single Aluminium Foil | Plain foil | Facing other insulation, vapour barrier |
| Double-Sided Foil | Foil both faces | Reflects both sides |
| Bubble Foil | Foil + air bubble core + foil | Roof / wall, adds small R-value |
| Foam-Backed Foil (XLPE/EPE) | Foil + polyethylene foam | Roof under-deck, ducts |
| Woven / Reinforced Foil | Foil + woven scrim | Tear-resistant, roofs |
| Foil + Glass Wool | Composite | Thermal + radiant combo |
| Property | Value |
|---|---|
| Reflectivity | 95–97% |
| Emissivity | 0.03–0.05 (low) |
| Thickness | 3–10 mm (bubble / foam types) |
| R-Value (with air gap) | ~1.0–1.5 (system, depends on gap) |
| Vapour Barrier | Yes (foil) |
| Weight | Very light |
| Water Resistance | High (foil) |
| Fire Behaviour | Foil non-combustible; core combustible (use FR) |
| Parameter | Reflective Foil | Bulk (Wool / Foam) |
|---|---|---|
| Mechanism | Reflects radiation | Resists conduction |
| Air Gap Needed | Yes (essential) | No |
| Thickness | Thin (3–10 mm) | Thick (25–100 mm) |
| R-Value (standalone) | Low | High |
| Best Climate | Hot (radiant heat) | All |
| Vapour Barrier | Yes | No (unless faced) |
| Cost | Low-Medium | Varies |
Best results combine both: reflective foil (radiant) + bulk insulation like glass wool or EPS (conductive).
| Brand | Products |
|---|---|
| Supreme | Insu-Reflect, foil insulation |
| Aerolam | Aerolam reflective insulation |
| Insulnergy | Reflective foil products |
| U-Tech | Bubble foil, XLPE foil |
| Reflectix | Reflective bubble (imported) |
| LERAFLEX / Cosmofil | Foil insulation |
| Standard | Description |
|---|---|
| ASTM C1224 | Reflective Insulation for Building Applications |
| ASTM E408 / C1371 | Emissivity Measurement |
| ASTM C1313 | Sheet Radiant Barriers |
| ASTM E84 | Surface Burning Characteristics |
| ISO 9050 | Solar Reflectance |
| ECBC 2017 | Roof / Building Insulation |
| Type | Cost |
|---|---|
| Single Foil (per sqm) | Rs 20 – 50 |
| Bubble Foil (per sqm) | Rs 35 – 90 |
| Foam-Backed Foil 4–6 mm (per sqm) | Rs 50 – 120 |
| Double-Sided / Reinforced (per sqm) | Rs 60 – 140 |
| Foil + Glass Wool Composite (per sqm) | Rs 80 – 180 |
| Installed (per sqft, roof) | Rs 12 – 35 |
Reflective foil insulation is highly effective at blocking radiant solar heat — ideal for Indian roofs, metal sheet roofs and sun-facing walls. It is thin, light, doubles as a vapour barrier, and is cheap, but it only works with an air gap and offers little resistance to conductive heat. For best results, combine reflective foil (radiant) with bulk insulation (conductive).
Pair with bulk insulation like glass wool, rock wool, EPS or XPS; for gap-filling, see PU foam.