Polycarbonate vs Glass Greenhouse: Light, Heat, Safety and Upkeep Compared
The glazing is the biggest decision in a greenhouse kit. It sets how much light your plants get, how warm the space stays at night, how it handles hail and kids' footballs, and how it looks in the yard. The two main choices are polycarbonate (a tough plastic, usually twin-wall) and glass (horticultural or tempered).
Quick answer
- Most hobby growers, cold or stormy climates, yards with kids or pets: twin-wall polycarbonate. It insulates better, diffuses light, and won't shatter.
- Maximum light, a permanent showpiece, or mild climates: tempered glass. It stays clear for decades and looks like a classic greenhouse.
- Hot, sunny summers: polycarbonate's diffused light scorches seedlings less, but either kind needs vents and shade cloth.
Side-by-side
| Twin-wall polycarbonate | Glass (tempered or horticultural) | |
|---|---|---|
| Light | Diffused; a little less total light, with fewer hot spots | Clear, direct light; the most light of any glazing |
| Insulation | Noticeably better, thanks to the air channel between walls | Single-pane glass loses heat fast at night |
| Impact and hail | Very impact-resistant | Tempered glass is strong but can break; horticultural glass breaks into sharp shards |
| Weight | Light, so the frame and base can be simpler | Heavy; needs a solid, level foundation |
| Lifespan | Often about 10–15 years before UV yellowing or brittleness (check the UV-coating warranty) | Decades; the glass itself doesn't degrade in sunlight |
| Looks | Frosted, utilitarian | Classic and see-through |
| Cleaning | Soft cloth only; abrasives scratch it. Algae can grow in the channels if the ends aren't taped | Easy to clean and hard to scratch |
| Relative cost | Usually lower for the same size | Usually higher, plus a sturdier base |
Light: more isn't always better
Glass lets in the most light, which helps in cloudy northern winters. But direct light also creates hot spots and leaf scorch in summer. Twin-wall polycarbonate scatters light so it reaches lower leaves and the back benches more evenly. Many growers in sunny regions see that as a plus, not a trade-off.
Heat: the night-time difference
The air gap in twin-wall panels slows heat loss, so a polycarbonate greenhouse stays warmer after sunset and needs less heating to keep frost out. If you plan to grow through winter, compare panel thickness: 4 mm is common in beginner kits, while 6 mm or 8 mm panels insulate better in cold zones. Single-pane glass greenhouses often add bubble-wrap insulation in winter, which cuts some of the light advantage.
Safety, hail and wind
- If you get hail, have kids playing ball nearby, or sit under trees that drop branches, polycarbonate is the safer bet.
- If you choose glass, pick tempered (safety) glass, which breaks into small blunt pieces, rather than standard horticultural glass.
- Either way, anchor the frame. Light polycarbonate kits are more likely to shift in strong wind if they aren't fixed down.
Upkeep over the years
Polycarbonate panels should come with a UV-protected outer face; install that side facing out, as the manufacturer marks it. Seal the channel ends with vented tape to keep out dirt and algae. Glass mainly needs cleaning and the odd glazing clip replaced. Expect to replace polycarbonate panels at some point in a greenhouse's life, while glass panes are usually replaced only when one breaks.
Which should you pick?
| If you… | Choose |
|---|---|
| Want to grow through a cold winter | 6 mm+ twin-wall polycarbonate |
| Get hail or have kids and pets in the yard | Polycarbonate |
| Want a permanent, decorative greenhouse | Tempered glass on a solid base |
| Garden in a cloudy region and want maximum light | Glass, plus winter insulation |
| Are buying your first greenhouse | Polycarbonate (see our beginner greenhouse kit guide) |
Check current price: Twin-wall polycarbonate greenhouse kits (retailer link coming soon)
Check current price: Tempered glass greenhouse kits (retailer link coming soon)
Check current price: Greenhouse shade cloth (retailer link coming soon)
Want to plan the space first? Our greenhouse plans and garden planner include layout grids.
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