Polycarbonate U-Value and Thermal Performance: Complete Spec Table for Glazing Buyers
Why U-Value Matters for Polycarbonate Glazing
The U-value (thermal transmittance, W/m²·K) tells you how much heat passes through a panel per square metre per degree of temperature difference. Lower is better for insulation. For polycarbonate, the U-value is set by the wall structure (number of walls, rib spacing, thickness) — not by the raw polymer. This is why multiwall PC out-insulates glass and single-layer sheet despite using the same material.
U-Value Comparison Table
| Glazing type | Thickness | U-value (W/m²·K) | Light transmission |
|---|---|---|---|
| Single glass | 6 mm | 5.8 | 90% |
| Double glazing (air) | 24 mm | 2.8–3.0 | 80% |
| Solid polycarbonate | 4–10 mm | 5.0–5.5 | 88–92% |
| Twin-wall PC | 6 mm | 3.5–3.9 | 80–82% |
| Twin-wall PC | 10 mm | 2.9–3.2 | 79–81% |
| Twin-wall PC | 16 mm | 2.4–2.7 | 75–80% |
| 6-wall PC | 16 mm | 2.0–2.3 | 65–75% |
| 6-wall PC | 25 mm | 1.6–1.9 | 55–65% |
Values are indicative per EN 673 (glass) and manufacturer data for PC. Exact U-values depend on rib geometry; request the certified value for the specific profile.
How U-Value Relates to Real Performance
- Greenhouse heating cost: a 16 mm 6-wall panel (U≈2.1) saves ~45% heating vs 6 mm twin-wall (U≈3.7) on the same area
- Condensation: lower U-value panels stay warmer on the inside face, reducing condensation in cold climates
- Solar gain: U-value is only half the thermal story — light transmission and solar heat gain (SHGC) matter for greenhouses and daylighting
- Combined metric: for energy modelling, use U-value + SHGC together, not U-value alone
Standards and Measurement
- EN 673 — U-value calculation for glass (methodology)
- ISO 10292 — heat transmittance of glazing
- EN 12631 / ISO 10077-2 — thermal performance of profiles (for framed assemblies)
- NFRC 100 — North American U-factor rating procedure
How to Specify for Thermal Performance
- Set your U-value target — from building code (e.g. roof glazing max U) or energy budget
- Choose wall structure — twin-wall for economy, 6-wall for insulation-first projects
- Match thickness to span — 10 mm twin-wall spans ~1.0 m; 16 mm spans ~1.4 m
- Add IR/thermal sheets — for the lowest U-values, specify IR-reflective or coated multiwall
- Confirm the certified value — request the manufacturer’s U-value certificate for your profile, not the generic table
FAQ: Polycarbonate U-Value
What is the U-value of 10mm twin-wall polycarbonate?
Approximately 2.9–3.2 W/m²·K, depending on the rib geometry. That is roughly equivalent to double glazing and about half the heat loss of single glazing.
Is polycarbonate better insulated than glass?
Single-skin polycarbonate is similar to single glass (~5 W/m²·K). Multiwall polycarbonate (16–25 mm) outperforms single and double glazing, reaching U-values of 1.6–2.3 W/m²·K.
What U-value do I need for a greenhouse?
For year-round heated greenhouses, target U ≤ 3.0 W/m²·K (10–16 mm multiwall). For unheated or seasonal structures, 6–10 mm twin-wall is the common balance of cost and performance.
Does a lower U-value reduce light?
Generally yes — more walls and thicker structures that insulate better also transmit less light. 25 mm 6-wall transmits ~55–65% vs 80%+ for 10 mm twin-wall. Balance insulation vs daylight for your crop or building use.
Solar Heat Gain (SHGC) — The Other Half of the Story
U-value measures heat loss; SHGC (solar heat gain coefficient) measures how much solar energy enters. For greenhouses and daylighting, SHGC is often more important than U-value:
| Glazing | U-value (W/m²·K) | SHGC | Light transmission |
|---|---|---|---|
| Clear twin-wall 10 mm | 3.0 | 0.70–0.75 | 80% |
| Diffused twin-wall 10 mm | 3.0 | 0.60–0.68 | 70–75% |
| 6-wall 16 mm | 2.1 | 0.50–0.60 | 65–70% |
| IR-reflective 16 mm | 1.7–1.9 | 0.40–0.50 | 55–60% |
Rule of thumb: hot climates — pick lower SHGC to reduce cooling load; cold climates — pick higher SHGC to harvest solar gain. The diffused surface option raises haze and softens light for greenhouse crops while barely changing U-value.
Condensation Control
- Anti-condensation coating — available on multiwall inner faces; bead-and-channel design drains interior condensation
- Ventilation — ridge and eave vents remove humid air, the real cause of internal condensation
- Sealed ends — open multiwall channels act as condensation traps; end caps or tape are mandatory
- U-value and dew point — lower U-value panels keep the interior face warmer, raising the condensation threshold
Energy Modelling Inputs for Designers
When you model a polycarbonate glazing project, use these inputs:
- U-value — from the certified manufacturer data (not the generic table)
- SHGC — from the specific product data sheet
- Air leakage — framed assemblies leak at joints; add 10–15% to effective U-value for modelling
- Thermal bridging — aluminium frames conduct heat; use thermally broken profiles for best performance
Get Thermal Performance Data for Your Project
Send your application (greenhouse, glazing, cold store), U-value target, span and climate. Bakway provides certified U-value data for our multiwall profiles and recommends the thickness/structure that meets your energy budget.