Polycarbonate vs. Glass Greenhouses
Glass is beautiful and transmits a little more light. Twin-wall polycarbonate insulates better, survives hail, and costs less to live with. Here is the fair fight.
The comparison at a glance
| Twin-wall polycarbonate | Horticultural glass | |
|---|---|---|
| Impact resistance | Flexes under hail, branches and stray balls; rarely breaks | Cracks or shatters on hard impact |
| Weight | Light; easy to handle and gentler on the frame | Heavy; needs a stronger frame and more hands |
| Insulation | Two walls with an air gap, like a double-pane window | Single pane loses heat fast (double glazing exists, at a steep price) |
| Light transmission | About 85% | Around 90% |
| Light quality | Diffused: spreads light, no hot spots | Direct: brighter, but can scorch leaves under panes |
| Maintenance | Rinse with water; can scratch if scrubbed abrasively | Stays optically clear for decades; individual panes replaceable but fragile |
| Installation | Light panels slide into channels; DIY friendly | Heavy, fragile panes; slower, often professional work |
| Cost over time | Lower up front, cheap panel replacements | Higher up front, cut glass replacements add up in hail country |
| Wind and snow | Light, flexible, held along full edges | Rigid and heavy; breakage risk in storms |
| Looks | Slightly translucent, modern | Fully transparent, the classic look; wins on pure aesthetics |
The rest of this article unpacks the rows that decide real purchases: light, insulation, durability and cost.
Light: glass transmits more, polycarbonate distributes better
Clear horticultural glass transmits around 90% of light; twin-wall polycarbonate about 85%. On paper, glass wins.
In a greenhouse, the picture is subtler. Glass passes light directionally: bright beams, sharp shadows, and hot spots that can scorch the leaves directly under the brightest panes on a summer afternoon. Polycarbonate diffuses light as it passes through the twin walls, spreading it across the whole growing space, including the undersides of leaves and the plants in the corners. Growers use shade cloth precisely to tame direct summer light; diffusion does part of that job for free.
The honest verdict: the 5 point difference is real, and in practice it is rarely the thing that decides how your plants do.
Insulation: the biggest practical difference
Twin-wall polycarbonate is two sheets with an air chamber between them, and that trapped air works exactly like the gap in a double-pane window. A single pane of glass, by contrast, is one of the fastest heat-losing surfaces there is.
What that means in a season: the polycarbonate greenhouse holds its daytime warmth further into the evening, frost arrives later inside, and the growing season stretches at both ends. If your reason for buying a greenhouse is more weeks of growing, insulation is the row of the table that should weigh most. How the twin-wall structure does this is covered in how twin-wall polycarbonate works.
Durability: hail is the honest test
Hail, a falling branch, a baseball, a mower-thrown stone: glass cracks or shatters, polycarbonate flexes and springs back. This is not a knock on glass; it is simply what the materials are. If you have kids, dogs, storms or hail in your life, the calculation makes itself.
Polycarbonate's own weakness is UV degradation: cheap, untreated sheet yellows and goes brittle within a few years. Quality panels carry a UV-protective layer on the outer face, which is what keeps them clear for the long haul. That coating is the single thing worth checking on any polycarbonate greenhouse, ours included: our panels are UV-protected and installed coated side out.
Cost over the years
Polycarbonate costs less up front, and its repairs are cheap: a replacement panel rather than a pane of cut glass. Glass costs more to buy, more to transport, and more every time weather or accident claims a pane, but a well-kept glass house keeps its optical clarity for decades.
Budget honestly for your climate: in hail country, glass ownership carries a recurring cost that polycarbonate simply does not have.
When glass is the right answer
Glass earns its keep when aesthetics lead the decision: a Victorian-style conservatory, a showpiece garden, a structure attached to the house. In a mild climate with little hail, and with the budget for the heavier structure it demands, a glass house is a beautiful thing and we will not pretend otherwise.
For a working backyard greenhouse in most of the United States, twin-wall polycarbonate is the material we build with, because it wins the rows that decide daily life: insulation, resilience and cost. Every Greenlyhouse model is glazed in 6 mm twin-wall polycarbonate as standard.
Your questions, in short
Untreated polycarbonate does. Panels with a UV-protective outer layer resist yellowing for many years. Our panels are UV-treated and installed with the coated side facing out.
On our frames, no. The channels are sized for polycarbonate thickness, and mixing materials creates sealing problems where they meet.
Yes. Light-hungry summer crops grow well under twin-wall polycarbonate, and the diffusion means fewer scorched leaves at the height of summer. In winter, keep the panels clean, because short days leave no light to spare.
Quality UV-protected twin-wall panels stay clear and serviceable for many years, and each panel is individually replaceable if one is ever damaged. Our greenhouses carry a 10-year warranty.
