Insulation - Closed Cell

Closed-cell insulation plays a critical role in high-performance building envelopes, offering superior thermal resistance and moisture control. Unlike open-cell products, closed-cell materials form tightly packed, gas-filled cells during manufacturing, resulting in higher density and lower thermal conductivity.

These materials are generally hydrophobic, meaning they do not allow water vapour to pass through. However, some closed-cell products may degrade over time when exposed to moisture or water vapour, so careful specification is essential—particularly when used in assemblies requiring vapour diffusion. When incorrectly installed, these materials can inadvertently trap moisture, increasing the risk of condensation and mould.

Closed-cell insulation is highly efficient across the insulated surface but sensitive to installation quality. Poor cutting or gapping between boards can significantly reduce thermal performance. Many foam board products are foil-faced to enhance vapour resistance and reflect radiant heat. When correctly taped with foil tape, these layers can improve airtightness, though they cannot compensate for poorly fitted joints.

Phenolic Foam (PF)

Phenolic foam is made from phenolic resin and a blowing agent like pentane. It’s known for its fine closed-cell structure and excellent insulating properties.

• Thermal conductivity: 0.022 – 0.040 W/m·K

• Density: ~40 kg/m³

• Key benefits: Low thermal conductivity, good fire performance

• Limitations: Brittle, difficult to cut, limited supplier availability

Polyurethane Rigid Foam (PUR)

PUR is created from polyol and polyisocyanate, producing a high-performing, durable foam.

• Thermal conductivity: 0.024 – 0.030 W/m·K

• Compressive strength: Up to 500 kPa

• Key benefits: High compressive strength, excellent thermal performance, chemical and solvent resistance

• Limitations: Susceptible to long-term degradation from moisture if not protected

Polyisocyanurate (PIR)

PIR is a modified form of PUR with enhanced fire resistance and thermal stability. It’s widely used in flat roofing, wall, and floor insulation.

• Thermal conductivity: 0.021 – 0.026 W/m·K

• Key benefits: Superior thermal resistance, better fire performance than PUR

• Limitations: Brittle in cold conditions, sensitive to moisture at edges if not foil-faced

Expanded Polystyrene (EPS)

EPS is made by expanding polystyrene beads with steam. It’s lightweight and cost-effective, commonly used in insulated concrete forms, cavity wall insulation, and underfloor systems.

• Thermal conductivity: 0.030 – 0.040 W/m·K

• Density: Typically 10 – 30 kg/m³

• Key benefits: Affordable, moisture resistant (with proper detailing), good compressive strength for low-load applications

• Limitations: Lower thermal performance compared to PIR and PUR, combustibility unless treated

Extruded Polystyrene (XPS)

XPS is manufactured through an extrusion process, giving it a uniform closed-cell structure and superior moisture resistance compared to EPS.

• Thermal conductivity: 0.029 – 0.035 W/m·K

• Density: 25 – 45 kg/m³

• Key benefits: High compressive strength, low water absorption, good long-term R-value retention

• Limitations: Higher cost than EPS, combustible unless protected