Glass vs Polycarbonate Greenhouse (2026)

Glass gives you about 90 percent light transmission, a clear view, and a panel that lasts decades. Twin-wall polycarbonate gives you roughly 80 percent light (diffused), about double the insulation, and a wall that laughs off hail. That is the whole decision in two sentences, and neither one is the right answer for everyone. It is a climate-and-use question, not a quality question.

We don't sell greenhouses. We save you from buying the wrong one, and getting glazing wrong is expensive twice: once when you pay for it and again when it cracks, yellows, or bleeds heat all winter. This page keys the choice to your climate, your hail risk, and how you actually garden.

The glazing choice also moves the budget more than most buyers expect, so read it next to the real cost of a greenhouse. If safety is your worry, glass safety covers tempered versus horticultural glass and the falling-glass hazard, served straight.

Quick Answer: Glass vs Polycarbonate at a Glance

Dimension	Glass	Twin-wall polycarbonate	Triple / multi-wall poly
Light transmission	~90%, crystal clear	~80%, diffused	~65%, fully diffused
Insulation (R-value)	~0.9 single pane	~1.7	R-2.0 to R-2.8
Hail and impact	Cracks, shatters	Very resistant	Very resistant
Safety	Falling-glass hazard unless tempered	Shatter-resistant	Shatter-resistant
View out	Clear	Cloudy/diffused	None, fully diffused
Lifespan	Decades, panel does not yellow	10+ yrs, yellows over time	10+ yrs, yellows over time
Look	Formal, heirloom	Utility	Utility
Relative price	Higher	Lower	Mid

Figures are typical industry values and worth verifying at write time against the specific product. Real light and R numbers vary with panel thickness and coatings.

Light: Glass Wins on Clarity, Poly Wins on Even Spread

Glass transmits the most light, around 90 percent, and it does it clear, so you see through it and the light comes in direct. That is why display and show greenhouses use it. Polycarbonate transmits a bit less, around 80 percent for twin-wall and lower for multi-wall, but the light it lets through is diffused, spread evenly so it reaches the lower leaves and reduces hot spots and leaf scorch. For growing, diffused light is often better, not worse. Solexx twin-wall polyethylene leans hardest into this, fully diffused, and university tests it cites show faster growth under that even light. The tradeoff is honest: with multi-wall poly you gain diffusion and insulation but lose the clear view, and some buyers dislike the cloudy walls.

Insulation: Polycarbonate Is Roughly Twice the Glass

This is where polycarbonate pulls ahead for cold climates. Single-pane glass sits around R-0.9, twin-wall polycarbonate around R-1.7, triple-wall R-2.0 and up, and thick 16mm multi-wall near R-2.8. That air gap between the walls is doing the work. In practice, a twin-wall house holds heat far better than a single-glass one, which means lower winter heating bills and steadier overnight temperatures for the season-extension grower. If you are in the Mountain West, the Upper Midwest, or the Northeast and plan to push the season into the cold, insulation is probably the single most important glazing factor, and it points to polycarbonate. The heating-cost math by glazing is in greenhouse heating cost.

Hail, Wind, and Safety: Polycarbonate's Clear Advantage

Polycarbonate is close to unbreakable by comparison. It flexes under impact where glass cracks or shatters, so in hail country or under a tree that drops branches, poly is the safer, cheaper-over-time material. It is also the safer material overhead: a shattered glass roof pane is a falling-glass hazard, which is why any glass greenhouse worth buying uses tempered (toughened) safety glass that breaks into blunt pieces, not horticultural glass. Cheap kits that use thin horticultural glass or brittle single-wall plastic fail on both counts. If a stray ball, a hailstorm, or kids in the yard are part of your reality, polycarbonate removes the worry. The full breakdown is in glass safety.

Lifespan and Looks: Glass's Advantage

Glass does not yellow. A quality glass panel stays clear for decades, which is why heirloom glasshouses are glazed in it and warrantied for 25 to 30 years. Polycarbonate, by contrast, yellows and clouds slowly under UV over 10 to 15 years and the panels are the part you eventually replace, though good panels carry UV coatings that slow it. And there is no contest on looks: glass under an aluminium or a painted frame reads as a formal, permanent glasshouse, while polycarbonate reads as a working structure. If the greenhouse is a feature of the garden and you want it to look the part for 20 years, glass earns its premium.

Cost: Poly Lower to Buy, Glass Longer to Live

Polycarbonate kits are cheaper to buy and lighter to ship and handle, which is why the mid-market lane, Palram/Canopia, Yoderbilt, Solexx, is almost all polycarbonate or polyethylene. Glass costs more up front, weighs more, and usually wants a stronger base under it. Over a very long horizon the glass panel outlives several poly re-glazings, so the "cheaper" material depends on your time frame. Either way, remember the glazing is only one line. The base, anchoring, and ventilation are the same job regardless of glazing, and they are in the real cost of a greenhouse.

Which One Fits You

Choose glass if you want the clearest light and view, a formal heirloom look, and a structure warrantied for decades, and you are budgeting a premium glasshouse with a proper base. Tempered glass, always, for safety. See best greenhouses and Hartley vs Alitex.

Choose twin or triple-wall polycarbonate if you garden in a cold, snowy, or hail-prone climate, you want lower heating bills and even diffused light, and you would rather spend less and grow the same plants. This is the right call for a lot of buyers. See best polycarbonate greenhouses.

Choose Solexx polyethylene if insulation and diffused light matter more than a clear view, especially for cold-climate season extension. You trade seeing through the walls for one of the higher R-values on the market.

Still weighing frame material alongside glazing? That is the other type decision, covered in aluminium vs wood frame. Get both settled and your brand shortlist writes itself.

Frequently Asked Questions

Is glass or polycarbonate better for a greenhouse?

Neither is better outright, they win on different things. Glass gives about 90 percent clear light, the best looks, and a decades-long lifespan, but insulates poorly and cracks under hail. Polycarbonate gives around 80 percent diffused light, roughly double the insulation, and near-unbreakable hail resistance, but it yellows over time and you cannot see through it. Cold or hail-prone climate points to polycarbonate, light clarity and a formal look point to glass.

Does polycarbonate really insulate twice as well as glass?

Close to it, yes. Single-pane glass is roughly R-0.9 and twin-wall polycarbonate is about R-1.7, so you are getting roughly double the insulation from the air gap between the walls. Triple-wall and thick multi-wall poly go higher still, up to about R-2.8. That difference shows up directly on your winter heating bill and in steadier overnight temperatures, which is why polycarbonate is the usual pick for cold-climate season extension.

Will polycarbonate panels turn yellow and cloudy over time?

Yes, slowly, over roughly 10 to 15 years under UV, and the panels are the part you eventually replace rather than the frame. Good polycarbonate carries a UV-protective coating that slows the yellowing considerably, so quality matters here. Glass, by contrast, does not yellow at all, which is one reason heirloom glasshouses use it. Factor a possible re-glazing into a polycarbonate house's long-term cost.

Is a glass greenhouse dangerous if a panel breaks?

Only if it is the wrong glass. A quality greenhouse uses tempered (toughened) safety glass, which breaks into small blunt pieces rather than long shards, so a broken roof pane is far less of a falling-glass hazard. Cheap kits that use thin horticultural glass are the real risk, and so is brittle single-wall plastic. If safety near kids or overhead panes is a concern, tempered glass or polycarbonate both solve it. The detail is in glass safety.

Which is better for hail and heavy weather?

Polycarbonate, clearly. It flexes under impact where glass cracks or shatters, so in hail country or under trees that drop branches it is the more durable and cheaper-over-time material. Glass can absolutely survive if it is tempered and the greenhouse is well built, but a bad hailstorm is exactly the event that turns a glass roof into a repair bill. If hail is a regular part of your weather, poly removes the worry.

Does diffused polycarbonate light grow plants worse than clear glass?

No, and often the opposite. Diffused light scatters evenly through the greenhouse so it reaches lower leaves and reduces hot spots and scorch, which many growers find produces more even growth than direct light through clear glass. What you lose with diffusion is the clear view out and the crisp look. For pure plant growth, diffused polycarbonate or Solexx is a genuine strength, not a compromise.