Overview of greenhouse coating materials
The covering is the material over your greenhouse frame that light passes through — and it largely decides appearance, functionality, cost and maintenance. The short answer: twin-wall polycarbonate is the most popular all-round choice (strong, insulating, 7–10 years of good performance), polyethylene film is the cheapest way to cover a greenhouse, and glass wins on clarity and lifespan if your frame and budget can carry it. Here are the six common options with their technical numbers.
How do greenhouse covering materials compare?
| Material | Light transmission* | R-value** | Lifespan |
|---|---|---|---|
| Glass, single layer | 85–90% | 0.9 | Unlimited (if unbroken) |
| Glass, sealed double layer | 70–75% | 1.5–2.0 (low-e 2.5) | Unlimited (if unbroken) |
| Polyethylene, single film | 80–90% | 0.87 (6 mil) | 1–2 years (UV film) |
| Polyethylene, double film | 60–80% | 1.5–1.7 | 1–2 years (UV film) |
| Polycarbonate, twin-wall | 83% | 1.6–1.7 | 7–10 years |
| Polycarbonate, triple/quad wall | 75% | 1.8–2.5 | 7–10 years |
* Light transmission: the percentage of light that enters the greenhouse through the material. ** R-value: a standard insulation measure (hr·°F·sq.ft/Btu) — the higher, the more heat stays inside.
1. Glass — single or sealed double layer
Single-layer glass gives the highest light transmission (85–90%) and lasts indefinitely if it doesn't break; tempered glass is stronger and needs fewer support bars. Factory-sealed double glazing trades some light (70–75%) for two to three times the insulation, making it usable in cold climates.
Pros: unlimited lifespan, unmatched clarity, double glazing suits low temperatures. Cons: fragile and may not carry snow loads, needs many supports (single) or heavy, precise framing (double), and clear glass doesn't scatter light — plants can get hot spots.
2. Polyethylene film — single or double layer
The cheapest covering and the easiest to install — no precise framing needed. Modern films come IR-treated to cut heat loss, anti-drip/anti-fog to resist condensation, and EVA-treated against cracking in cold weather. A double layer with a small fan keeping an air gap between films significantly reduces heat loss (R 1.5–1.7 vs 0.87).
Pros: lowest cost, quick installation, good light transmission when new, treated films fight condensation and heat loss. Cons: tears easily, hazes over time, expands and contracts with temperature, and UV-resistant film still needs replacing every 1–2 years.
3. Polycarbonate — twin, triple or quad wall
Rigid multi-wall sheets combine strength, insulation and workability: 83% light transmission in twin-wall, rising R-values with more walls (up to 2.5 at 16 mm triple-wall). It is the most fire-resistant covering, UV-resistant, very strong yet light, easy to cut and install, and performs well for 7–10 years — the reason it has become gardeners' favourite in recent years.
Pros: strong, insulating, light-diffusing, easy to work with, long service life. Cons: can be expensive, and it is only partially transparent — you won't get glass-like clarity.
Which covering should you choose?
Match the material to your budget, climate, location and how you'll use the greenhouse: glass for permanence and maximum light, polyethylene for the lowest cost and easy DIY, polycarbonate for the best durability-to-insulation balance. Remember the covering also shapes your watering: better-insulated coverings hold heat and humidity longer, so soil dries at a different pace through the season — another case where moisture-based watering beats a fixed schedule.
Frequently Asked Questions
What is the best all-round greenhouse covering?
Twin-wall polycarbonate — 83% light transmission, R-value around 1.6–1.7, very strong, and 7–10 years of good performance at a mid-range price.
How often does polyethylene film need replacing?
UV-resistant film typically lasts 1–2 years; light transmission drops as it ages, so plan on regular replacement.
Does the covering affect how much I need to water?
Yes — higher R-value coverings keep heat and humidity in, slowing soil drying, while single films lose both quickly. Soil-moisture sensors adjust watering to the real conditions under your covering.