4 mm, 6 mm, 8 mm or 10 mm Polycarbonate Greenhouse Panels: A Buyer’s Specification Framework

Polycarbonate (PC) panels are the glazing material for most aluminum-frame greenhouses sold in the home garden market. Solid PC sheet is approximately one-sixth the weight of glass of the same thickness; twin-wall and multi-wall panels are lighter still due to their hollow structure. PC is nearly unbreakable and provides better insulation than single-layer glass. But “polycarbonate panel” is not a single product. The thickness, wall structure, UV protection, and panel weight all vary, and each of these variables affects performance, cost, and suitability for different climates and greenhouse sizes.

A buyer who only compares panel thickness is missing most of the specification.

Why Panel Thickness Is Only One Part of the PC Sheet Specification

Panel thickness — 4 mm, 6 mm, 8 mm, or 10 mm — is the most commonly quoted PC panel specification, and it does matter. Thicker panels provide better insulation (higher R-value), greater impact resistance, and improved rigidity. But thickness alone does not tell you:

• Whether the panel is twin-wall (two walls with ribs between) or multi-wall (three or more walls with multiple rib layers)
• Whether the panel has a UV-protective co-extruded layer on one or both sides
• The density and weight of the panel (which affects both insulation value and freight cost)
• The light transmission percentage
• Whether the panel has been tested for impact resistance (e.g., Izod or falling-weight test data)

Two 6 mm panels from different manufacturers can have different wall structures, different UV protection, different light transmission, and different impact resistance. The thickness number is the starting point, not the complete specification.

Twin-Wall vs Multi-Wall Structure and Panel Weight

The internal structure of a PC panel — the arrangement of walls and ribs — affects both insulation and rigidity:

Twin-wall (double-wall) — Two parallel walls connected by vertical ribs. This is the most common structure for home garden greenhouses. Twin-wall panels in 4 mm and 6 mm thickness are the standard for entry-level and mid-range greenhouses. They provide good insulation (significantly better than single-layer glass) and adequate rigidity for panels up to about 1 m in unsupported span.

Triple-wall and multi-wall — Three or more walls with multiple rib layers. These structures provide better insulation and greater rigidity than twin-wall at the same thickness. A 10 mm triple-wall panel will have better insulation and stiffness than a 10 mm twin-wall panel. Multi-wall structures are more common in thicker panels (8 mm and above) and in greenhouses designed for colder climates or larger spans.

Panel weight — The weight of a PC panel depends on both the thickness and the wall structure. Typical industry specifications for 6 mm twin-wall panels range from approximately 1.0–1.3 kg/m², and 10 mm multi-wall panels may range from approximately 1.5–2.0 kg/m², though these values vary by manufacturer and wall structure — confirm actual weight on your approved sample. Panel weight affects both the structural load on the greenhouse frame and the freight cost per panel. Heavier panels require stronger frame profiles but provide better insulation.

The relationship between thickness, wall structure, and weight is not linear. A 10 mm twin-wall panel is not simply “better” than a 6 mm twin-wall panel — it is heavier, more expensive, and provides better insulation, but the improvement in impact resistance may be modest compared to the improvement from upgrading to a multi-wall structure at a lower thickness.

UV-Protected Surface, Light Transmission and Labeling

The UV-protective layer is the single most important factor in PC panel longevity. Without UV protection, polycarbonate panels will yellow, become brittle, and lose transparency within a few years of outdoor exposure. With a properly applied UV co-extruded layer, suppliers typically offer warranties of approximately 10 years — confirm the actual warranty period and coverage terms with your panel supplier.

Key points about UV protection:

One-sided application — The UV layer is typically co-extruded onto one side of the panel. This side must face outward (toward the sun) during installation. Installing the panel with the UV side facing inward is a common error that dramatically shortens panel life — from 10+ years to 2–3 years before visible degradation.

UV layer thickness — PC panel suppliers typically apply a UV co-extruded layer. The exact thickness varies by supplier — buyers should confirm the UV layer thickness and application method with the supplier rather than assuming a standard value.

Light transmission — PC panels typically transmit 80–85% of visible light for new twin-wall panels. Light transmission decreases over time as the panel ages, particularly if the UV layer is inadequate. For home garden greenhouses, 80%+ light transmission is generally sufficient for plant growth. Lower transmission (below 75%) may be a concern for light-hungry crops in shorter growing seasons.

Labeling — The UV-protected side should be clearly marked by the manufacturer. Common marking methods include printed text or arrows on the protective film, colored labels, or edge printing. The marking must survive the supply chain from panel manufacturer to greenhouse factory to end-user installation.

Insulation, Rigidity and Freight Trade-Offs

Choosing the right PC panel thickness and structure involves trade-offs:

For home garden greenhouses, 6 mm twin-wall is a commonly used choice — it balances insulation, rigidity, weight, and cost for the typical 5–10 m² greenhouse. 4 mm panels are used for smaller structures or markets where cost is the primary driver. 8 mm and 10 mm panels are used where additional insulation or impact resistance is needed, such as cold-climate markets or hail-prone regions. The appropriate thickness depends on the target climate, greenhouse size, and price positioning — not on a universal market rule.

What to Put on the RFQ and Approved Sample Record

When sourcing PC panels for a greenhouse, the RFQ and approved sample record should include:

• Panel thickness — e.g., 6 mm (specified with tolerance)
• Wall structure — twin-wall, triple-wall, or multi-wall
• Panel weight — kg/m², verified on the sample
• UV protection — co-extruded one-sided, with layer thickness confirmed by supplier
• UV side marking method — printed film, label, or edge printing
• Light transmission — percentage for new panel
• Impact test data — if available (e.g., falling-weight test or Izod impact strength)
• Panel dimensions — standard width, length, and cutting tolerance
• Color — clear, opal, or bronze (clear is standard for greenhouses)

The golden sample should be a full-size panel (or a minimum 30 × 30 cm cut sample) with the UV-protected side clearly identified. Store the sample away from direct sunlight to preserve it as a reference.

A complete PC panel specification is not complex, but it requires more than a thickness number. The thickness, wall structure, UV protection, and panel weight together determine how the panel will perform over its service life. Specify all of them, and verify on samples.