Polycarbonate U-Value Guide: Insulation Performance of PC Sheets (W/m²K, 2026)
4 mm twin-wall polycarbonate has a U-value of about 3.3 W/m²K; 10 mm twin-wall drops to 2.5 W/m²K; 16 mm triple-wall reaches 1.8 W/m²K; 25 mm 5-wall achieves 1.2 W/m²K. Compared with 4 mm twin-wall, 25 mm 5-wall cuts heat loss by roughly 64%.
Polycarbonate U-values by thickness and structure
| Sheet thickness & structure | U-value | Relative heat loss |
|---|---|---|
| 4 mm twin-wall | ~3.3 W/m²K | Baseline |
| 10 mm twin-wall | ~2.5 W/m²K | ≈24% lower heat loss than 4 mm |
| 16 mm triple-wall | ~1.8 W/m²K | ≈45% lower heat loss than 4 mm |
| 25 mm 5-wall (X-structure) | ~1.2 W/m²K | ≈64% lower heat loss than 4 mm |
U-value = heat lost per m² per degree of temperature difference. Lower is better: 1.2 W/m²K is roughly double-glazing performance, at a fraction of the glazing weight and cost.
How PC insulation compares with other glazing
| Glazing option | U-value (typical) | Light transmission |
|---|---|---|
| 4 mm twin-wall PC | ~3.3 W/m²K | ~80% |
| 10 mm twin-wall PC | ~2.5 W/m²K | ~72% |
| 16 mm triple-wall PC | ~1.8 W/m²K | ~65% |
| 25 mm 5-wall PC | ~1.2 W/m²K | ~55% |
| Single glass (4 mm) | ~5.8 W/m²K | ~90% |
| Double glazing (12 mm gap) | ~2.7 W/m²K | ~80% |
| Standard acrylic sheet (10 mm) | ~5.0 W/m²K | ~92% |
Polycarbonate multiwall is the only lightweight glazing that matches double glazing insulation without a heavy frame — one reason it dominates greenhouse and atrium roofing.
Greenhouse heating: what the U-value means for your energy bill
A 1,000 m² greenhouse roof in a 15°C heating season with 4 mm twin-wall loses roughly 50,000 kWh per season through the roof; upgrading to 10 mm twin-wall cuts that by about a quarter, and to 25 mm 5-wall by nearly two-thirds. At typical industrial electricity prices the payback on thicker multiwall is usually under two heating seasons.
Choosing the right structure for insulation
- Cold-climate greenhouses — 16 mm triple-wall or 25 mm 5-wall: best insulation per kg of installed glazing
- Skylights and atriums — 10–16 mm twin/triple-wall balances light and insulation
- Pool enclosures — 16–25 mm multiwall prevents condensation and holds humidity
- Noise barriers — solid PC (thermal performance secondary)
FAQ: Polycarbonate U-value and insulation
What is the U-value of 10 mm polycarbonate?
10 mm twin-wall polycarbonate has a U-value of about 2.5 W/m²K — roughly 24% better than 4 mm twin-wall (3.3 W/m²K) and comparable to double glazing.
Is polycarbonate a good insulator?
Yes. Multiwall polycarbonate achieves U-values from 3.3 down to 1.2 W/m²K depending on structure (4 mm twin-wall to 25 mm 5-wall). It is the standard lightweight insulator for greenhouses, skylights and pool enclosures.
What is the best polycarbonate for winter greenhouses?
16 mm triple-wall (1.8 W/m²K) or 25 mm 5-wall (1.2 W/m²K) are the best options for cold-climate greenhouses — they cut heat loss by 45–64% compared with 4 mm twin-wall while staying light enough for simple frames.
Does polycarbonate block more heat than glass?
Multiwall PC insulates better than single glass (3.3 W/m²K vs 5.8 W/m²K for 4 mm twin-wall vs single glass) and matches double glazing (2.7 W/m²K) at 10 mm thickness.
Will thicker polycarbonate reduce light too much?
Light transmission drops with wall count: ~80% at 4 mm twin-wall, ~65% at 16 mm triple-wall, ~55% at 25 mm 5-wall. For crops, pair thicker insulation with diffused-light films to keep growth rates high.
How do I calculate heating savings with a lower U-value?
Heat loss = U-value × area × heating degree-hours. Moving from 4 mm twin-wall (3.3) to 10 mm twin-wall (2.5) reduces roof heat loss by about 24%; to 25 mm 5-wall (1.2) by about 64%.
Related: sheet weight calculator · span & load chart
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