The short answer
There is no single right glazing — it depends on your priorities. Glass transmits the most light (around 90%), looks traditional and stays clear for years, but it is heavier, can shatter, and insulates less well. Polycarbonate transmits a little less light (roughly 76–82%) but spreads it more evenly, insulates noticeably better thanks to its hollow twin- or multi-wall structure, and is far more impact-resistant and shatterproof — useful where children, pets, falling debris or footballs are a factor. In short, glass favours light and looks, while polycarbonate favours warmth and durability. The right answer balances light, heat retention, safety and budget for your site.
The glazing choice is really a trade-off between light, warmth and toughness. Here is how the two compare on the things that matter for a UK garden.
At a glance
- Glass~90% light, clear, can shatter
- Polycarbonate~76–82% light, better insulation
- Best lightglass
- Best insulationpolycarbonate
- Best impact resistancepolycarbonate
How the glazing compares
Glass is the traditional choice and lets in the most light, which matters for year-round growing; toughened safety glass is common on modern aluminium models. Its downsides are weight, the risk of shattering, and weaker insulation. Polycarbonate is lighter, much harder to break, and its hollow-wall construction traps air to slow heat loss — twin- or multi-wall panels can reduce heat loss substantially compared with single-pane glass. It transmits a little less light overall but diffuses it more evenly, reducing scorch. The flip side is that cheaper polycarbonate can discolour or scratch over time and panels can flex in high wind if not well secured.
| Glazing | Light | Insulation | Durability |
|---|---|---|---|
| Glass (toughened) | highest (~90%) | lower | sturdy but can shatter |
| Twin/multi-wall polycarbonate | ~76–82%, diffused | higher | impact-resistant, shatterproof |
| Horticultural glass | high | lower | thin, breakable |
General comparison for guidance; figures depend on panel type and quality. Sources: glazing comparison guides.
How to choose for your garden
- Want maximum light and a classic look? glass is hard to beat, especially toughened safety glass.
- Want warmth and lower heating? polycarbonate's better insulation can help extend the growing season.
- Children, pets or an exposed spot? polycarbonate's shatter resistance is the safer choice.
- Tight budget? both have entry-level options; compare on panel type and thickness, not just the headline.
Want help choosing the glazing?
We'll match you with a vetted greenhouse supplier or installer who sets out the glazing options for your garden, with light, insulation and cost explained clearly.
Frequently asked questions
Is glass or polycarbonate better for a greenhouse?
It depends on your priorities. Glass transmits the most light (around 90%) and looks traditional, while polycarbonate insulates better and is far more impact-resistant and shatterproof. Glass favours light and looks; polycarbonate favours warmth and durability.
Does polycarbonate let in enough light for plants?
Yes for most growing. Polycarbonate transmits a little less total light than glass (roughly 76–82%) but diffuses it more evenly, which reduces scorch and spreads light around the greenhouse. Glass still leads on raw light transmission.
Is polycarbonate safer than glass?
Generally yes. Polycarbonate is impact-resistant and shatterproof, so it is the safer choice where children, pets, falling debris or high winds are a factor, whereas glass can shatter on impact.
Sources & further reading
- Greenhouse Stores — how much does a greenhouse cost UK 2026
- Greenhouse Emporium — glass vs polycarbonate greenhouse
Figures on this page are typical UK ranges drawn from published sources and depend on your specific garden and choices. They are guidance, not a quotation.