Multiwall polycarbonate (PC multiwall) is a panel built from two or more polycarbonate skins connected by internal ribs, forming hollow air channels. This cross-section gives the material an exceptional combination of light weight, impact strength and thermal insulation — which is why it has come to dominate the market for roofing, greenhouses, skylights and partitions. See the available thicknesses and colours of polycarbonate in our offer.
Construction and Panel Types
The internal structure of multiwall polycarbonate determines its insulation performance. More walls and chambers mean higher insulation values:
Twin-wall — 4, 6, 8, 10 mm
The most popular type. Two skins connected by vertical ribs. Available in 4–10 mm thickness.
- Light transmission: up to 82% (clear)
- Lightweight, easy to process
- Applications: patio canopies, hobby greenhouses, garden rooms
Triple-wall — 8, 10, 16 mm
Three skins, two chamber layers. Better insulation than twin-wall.
- Light transmission: approx. 72–78%
- Higher rigidity at the same thickness
- Applications: commercial greenhouses, industrial roof skylights
Multi-wall / X-structure — 16, 25, 32, 40 mm
Four or more skins, sometimes with diagonal ribs (X-structure). Best thermal insulation.
- U-value (16 mm, 3-wall): approx. 1.9 W/m²K
- U-value (25 mm, 5-wall): approx. 1.5 W/m²K
- Applications: building facades, large-area skylights, passive-house construction
Honeycomb — 10, 16 mm
Internal hexagonal structure. Exceptionally rigid for its weight. Less common; used in specialist constructions.
Properties of Multiwall Polycarbonate
| Feature | Value |
|---|---|
| Weight (10 mm, 3-wall) | ~1.7 kg/m² |
| Glass weight (6 mm) | ~15 kg/m² |
| Impact resistance | ~200× higher than glass |
| Temperature range | –40°C to +120°C |
| Fire behaviour | Self-extinguishing (class B1/B2) |
| UV protection | On the exposed-side skin (marked with film) |
| Light transmission | 40–82% (depending on colour and thickness) |
| Minimum cold-bend radius | approx. 150× panel thickness |
UV Protection — A Critical Installation Detail
Polycarbonate panels have a UV-protective coating on one side only — it is indicated by a protective film or an edge marking ("This side out" / "UV side"). Installing the panel the wrong way round causes material degradation, yellowing and brittleness within just a few seasons.
When CNC-cutting always check which side is marked and plan the orientation of the panel on the finished element.
CNC Cutting Parameters
Polycarbonate is harder and more ductile than acrylic — it does not crack during cutting, but produces long, stringy chips that can wrap around the cutter.
Milling and panel sizing
- Spindle speed: 12,000–18,000 rpm (lower than acrylic)
- Feed rate: 3,000–6,000 mm/min
- Cut depth: 50–100% of panel thickness (single pass is possible for panels up to 10 mm)
- Cutter: single-flute O-flute for plastics or a straight-flute PC cutter; avoid multi-flute cutters (chips do not evacuate cleanly)
- Cooling: compressed air directed at the cutting zone — evacuates chips and cools the edge
- Keep the protective film on during machining — it protects the surface from scratches
Specifics of the cellular structure
A cutter passing through multiwall polycarbonate alternates between material and air. This causes:
- Momentary vibration at each rib — reduce depth of cut for particularly precise cuts
- Inner skin tear-out if feed rate is too high
- Chamber deformation from heat if feed rate is too low
Best practice: a single full-depth pass at high feed rate (5,000–6,000 mm/min) with good chip evacuation using compressed air.
Drilling
- Standard plastic-specific drill bits (60–90° point angle)
- Speed: 1,500–3,000 rpm
- Fixing holes should be 3–4 mm larger than the screw/bolt diameter — polycarbonate expands thermally by approx. 0.065 mm/m/°C
Comparison with Other Glazing Materials
| Feature | PC multiwall (10 mm) | Glass (6 mm) | Acrylic (5 mm) |
|---|---|---|---|
| Weight | ~1.7 kg/m² | ~15 kg/m² | ~6 kg/m² |
| Insulation (U-value) | ~2.1 W/m²K | ~5.8 W/m²K | ~5.0 W/m²K |
| Impact resistance | ✓✓✓ | ✗ brittle | ✓ (cracks on impact) |
| UV transmission | ✗ (blocks UV) | ✓ (passes UV) | ✓ (passes UV) |
| Cold bending | ✓ | ✗ | ✗ |
| Service life | 10–15 years | 30+ years | 10–20 years |
| Price | $ | $$ | $$$ |
Key difference vs acrylic: polycarbonate blocks UV radiation — an advantage for canopies (protects furniture and skin) but a disadvantage in plant-growing greenhouses where full UV spectrum is needed.
Common Mistakes in Processing and Installation
1. Installing the panel upside down. Non-UV-protected side facing outward — the panel yellows and becomes brittle within 2–3 seasons.
2. Sealing chambers at the bottom. The channels in multiwall polycarbonate must drain condensate. Bottom edges are sealed with perforated tape (not airtight), top edges with solid aluminium tape.
3. Over-tightened fixings. No allowance for thermal expansion causes panels to buckle in summer. Fixing holes must be oversized (3–4 mm clearance), screws tightened without compressing the panel.
4. Insufficient overlap. Minimum cover when joining panels under a profile: 30–50 mm depending on roof pitch.
5. Cutting without chip extraction. Polycarbonate chips accumulate inside the chambers and are very difficult to remove afterwards. Use CNC with air blow or a circular saw with dust extraction.
Colours and Effects
- Clear (transparent) — maximum light transmission; plant greenhouses, industrial skylights
- Opal / milky — light diffusion, even interior illumination, canopies
- Bronze / smoke — solar heat and glare reduction; patios and gardens
- Green, blue — colour effects, decorative elements
- Bronze — elegant finish, popular for office-building enclosures
Applications
- Patio and garden canopies — lightweight self-supporting structures, hail-resistant
- Greenhouses and garden rooms — insulation, light transmission, low structural load
- Roof skylights — industrial and residential, replacing glass for safety benefits
- Partitions and dividing walls — interior and exterior; bus shelters, covered walkways
- Ventilated façades — modern cladding for office buildings and industrial halls
- Noise barriers — alongside motorways and railways, transparent or coloured
- Polytunnels and cold frames — agricultural applications, can support foot traffic
Planning a canopy, skylight or polycarbonate partition? Learn more about our CNC cutting and machining services, see our projects or request a quote — CNC workshop in Szczecin, delivery throughout Poland and the EU.