Greenhouses have now become a critical component of modern gardening. They extend the growing season, protect fragile plants, and increase year-round harvests. The decision on the structure of a greenhouse covering is a critical consideration, and no option is more versatile than polycarbonate sheets. Polycarbonate sheets have durable construction and provide strong light and UV protection, transforming greenhouse construction. With so many options, how then, do you pick the most appropriate thickness for your greenhouse?
While some may focus on the price and the aesthetics, the thickness of a polycarbonate sheet is critical for insulation, durability, energy, and plant health. This guide focuses on the most appropriate thickness of a polycarbonate sheet for use on greenhouses in your particular situation. This guide will aid in your decision, whether you are a hobbyist building a small greenhouse or a commercial grower. The balance of the climate, cost, and purpose of the greenhouse will assist in creating the most viable greenhouse environment.
What Are Polycarbonate Sheets and Why Choose Them for Greenhouses?
Before discussing thickness options, let us start with the fundamentals. Polycarbonate sheets are thermoplastic materials that are substitutes for glass or polyethylene film. Polycarbonate sheets are glass substitutes and are designed to be transparent or translucent. Polycarbonate sheets are virtually unbreakable and are 250 times stronger and lighter than glass. They also disperse light evenly, preventing the formation of hot spots, extremely warm areas that may burn and injure the foliage of plants.
For greenhouses, polycarbonate sheets excel in the following ways:
Superior Light Diffusion: They scatter and diffuse sunlight. This encourages uniform plant development and minimizes shadow creation.
Light Diffusion: Light is scattered and diffused toward plants. This prevents areas of shadow and encourages uniform development.
UV Protection: The good UV rays are let in. The bad UV rays are kept out. This is a plus for plants.
Thermal Insulation: Multi-wall structural designs trap air in pockets between walls and help in reducing temperature variances.
Longevity: There’s a guarantee of 10–15 years of little to no yellowing and weathering deterioration.
While single-layer plastic is a lightweight and low maintenance option for greenhouses, polycarbonate sheets improve upon this option greatly. Their modular nature and ease of cutting also mean they can be installed over all types of frames including hoop houses and rigid metal structures.
Examining the Thickness Options for Polycarbonate Sheets
The thickness options for polycarbonate sheets used for greenhouses range from 4mm to 25mm and can be in twin, triple, and quadruple configurations. The sheets are classified as ‘walled’ when they contain a predetermined number of hollow channels and insulated sheets trap heat by entraping air within. Single-walled sheets are uncommon as they tend to have poor thermal performance. Thus, we will focus on multi-walled sheets.
Here, we will outline the common thicknesses, their advantages, disadvantages, and best uses.
4mm Twin Polycarbonate Sheets
These light and thin sheets are flexible, and due to their lower price, they are popular with beginners.
Advantage
– The initial purchase price is approximately 20 to 30% lower than other options.
– Lighting transmission that goes as high as 90% works in your favor when growing sun-loving plants, such as tomatoes and herbs.
– Small projects as a result take less labor time, as it is easy to handle and install.
Disadvantages
Since there are no insulating features, extra winter heating costs are expected.
Can bow and break more easily under snow or wind load.
Best for:
Small and seasonal greenhouses located in warmer climates (USDA Zones 8–10). Perfect starter setups for extending the growing season in early spring and late fall.
6mm Twin- or Triple-Wall Polycarbonate Sheets
Our 6mm sheets are the most popular choice for hobbyists and mid-sized greenhouses, balancing performance and price.
Pros:
U-value around 3.5 W/m²K retains more heat for shoulder-season growing.
Provides good strength for moderate winds and light snow; retains ~85% light transmission.
Cost-effective upgrade offering 20–30% better energy savings.
Cons:
Whoever has them will be at risk during severe weather, and they will not perform well in heavily snowed climates.
Best for:
Small to medium greenhouses in temperate climates (Zones 6–8). Ideal for vegetables, flowers, and perennials that need consistent light and moderate warmth.
For 8mm Twin- or Triple-Walled Polycarbonate Sheets
8mm sheets outperform other sheets in higher-demand contexts.
Pros:
Excellent insulation (U-value ~3.0 W/m²K) minimizes condensation and frost buildup.
High impact resistance; withstands hail and winds over 50 mph.
Diffused light (82–86%) reduces excessive algae growth.
Cons:
30 to 50 percent higher costs than 6mm sheets; a heavier weight
Additional weight requires a more robust frame. Lower light transmission may require adding a grow light in less sunny areas.
Best for:
Larger hobby or smaller commercial greenhouses located in areas with moderate climate, infrequent light snowfall, or moderate light stormy weather. Excellent for full-year growing, especially for cooler season crops including: lettuce and strawberries.
10mm + Multi-Wall Sheets (Triple or Quadruple)
In insulated greenhouses, thicker (10mm or more) sheets will provide the best quality of insulation for the greenhouse.
Pros:
Outstanding insulation (U-value as low as 1.7 W/m²K for 16mm) can save up to 40% on winter heating costs.
Exceptional longevity; withstands snow loads of 20–30 psf and extreme winds.
Noise-canceling and anti-drip coatings on premium models keep the space quiet and clean.
Cons:
– High cost (50–100% more than 4mm) and heavier weight requiring reinforced structures.
– Lower light transmission (70–80% for 16mm+); supplemental led lighting needed.
Best for:
Commercial greenhouses or harsh climates (Zones 3–5), ideal for overwintering value crops like orchids and tropicals.
The Variation in U-Value and Insulation
Gours
U-Value (W/m²K)
10.0
2.3
12.0
2.5
15.0
3.0
U-values below 3.0 W/m²K offer good thermal insulation, while those near 1.0–2.0 provide excellent energy efficiency.
Cost Reduction and Energy Efficiency
There is an initial saving with thinner and cheaper sheets, but it will increase winter heating costs by 20–50%. Utility savings will allow a 10mm upgrade to pay for itself in 2–3 years. The cost of reinforced frames for thicker sheets will need to be considered.
Types of Plants and Purposes for Growing
4–6mm: Best for sun-loving plants like peppers.
10mm: Ideal for shade-tolerant plants like ferns.
12mm+: Excellent for tropical plants. Maintains stable humidity and temperatures which is a tropical plant prerequisite.
Maintenance and Durability
Thicker sheets require fewer repairs and will survive impact and debris. All polycarbonate sheets will degrade and UV fade, but 5 layers will be the most cost effective in the long run. Enhanced versions will have an anti-scratch layer to UV protection as well as to minimize maintenance.
Climate-specific recommendations
– Mild (Zones 8–11): 4–6mm twin-wall.
– Temperate (Zones 6–7): 6–8mm for balanced insulation.
– Cold (Zones 4–5): 8–10mm triple-wall for snow management.
Extreme Cold (Zones 1–3): 12–16mm quadruple-wall for storm resistance.
Always check local building codes.
Tips for Best Performance of Polycarbonate Sheets
Prepping the Frame: The frame of the structure should be level, square, and should be able to support the sheets. The best frames in case of corrosion are aluminum or galvanized steel.
Cutting and Handling: Use a utility knife, score and snap. Use gloves to prevent hazing and support edges for transport to prevent bowing.
Conclusion:
If you are choosing the appropriate thickness of a polycarbonate sheet depends on your climate, goals, and budget. If you are looking to buy polycarbonate sheets for your next work? Contact us and visit Wholesale POS for great pricing and knowledgeable assistance. The right thickness will turn your greenhouse into a year-round growing space.