The glazing material is the single biggest decision when choosing a greenhouse. Glass and polycarbonate are the two dominant options for permanent structures, and each has genuine strengths that make it the better choice for certain situations. Here’s the real comparison, without the marketing spin.
| Factor | Glass | Polycarbonate (twin-wall) |
|---|---|---|
| Light transmission | ~90% (single pane), ~80% (double) | ~80–83% (diffused) |
| Light quality | Direct, focused (can create hot spots) | Diffused (even distribution, no hot spots) |
| Insulation (R-value) | R-0.9 (single) / R-1.8 (double-pane) | R-1.5 (4mm) / R-2.5+ (8mm+) |
| Impact resistance | Low (breakable by hail, debris) | Very high (virtually unbreakable) |
| Lifespan | 30–50+ years | 15–25 years (UV-coated) |
| UV degradation | None | Yellows without UV coating (10–15 yrs) |
| Scratching | Highly scratch-resistant | Susceptible to surface scratches |
| Weight | Heavy (requires strong frame + foundation) | Lightweight (easier to ship and install) |
| DIY assembly | Difficult (fragile, precise fitting) | Moderate (weekend project for two people) |
| Aesthetic appeal | Classic, elegant | Functional, clean |
| Replacement cost | High (custom pane sizes) | Moderate (standard panel sizes) |
| Typical cost (8×12) | $$$ | $–$$ |
Glass is the right choice when aesthetics matter as much as function—if your greenhouse doubles as a garden feature, entertaining space, or architectural element. It’s also the best option if you’re building a permanent structure intended to last decades and you’re willing to invest in double-pane glass for insulation. Glass provides the highest light transmission of any glazing material, which matters in northern climates with limited winter sunlight.
The downsides are real: glass is expensive, heavy (requiring a substantial frame and foundation), fragile (hail and fallen branches are genuine risks), and single-pane glass is a poor insulator that drives up heating costs.
Polycarbonate is the better choice for most hobby growers. Twin-wall panels provide better insulation than single-pane glass at a fraction of the cost, with virtually no breakage risk. The diffused light that polycarbonate provides actually promotes more even plant growth than the direct, focused light of glass—fewer hot spots, fewer scorched leaves.
If you’re buying a kit greenhouse (the most common approach for hobby growers), polycarbonate is almost certainly what you’ll get. Brands like Palram/Canopia, Grandio, Rion, and Outsunny have refined polycarbonate greenhouse kits to the point where they’re reliable, well-documented, and straightforward to assemble.
The main polycarbonate concerns: panel yellowing over time (buy UV-coated panels from reputable brands), surface scratching (cosmetic, not structural), and a shorter lifespan than glass (15–25 years vs 30–50+, though replacement panels are inexpensive).
For the vast majority of home growers, polycarbonate wins on practicality. Better insulation per dollar, impact resistance, easier installation, and lower overall cost. Choose glass only if you have a specific reason—architectural aesthetics, maximum light transmission needs, or a budget that supports double-pane glass with the associated frame and foundation requirements.
For a deeper dive into all greenhouse types (including hoop houses and cold frames), see our Greenhouse Types guide.