How to Select and Buy Polycarbonate Sheet

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Polycarbonate sheet is popular with gardeners for use in greenhouses and cold frames. It comes in standard sizes that can be cut to size, or it can be made to order. It is a safer option than glass for those with young children and grandchildren. Here’s what else you need to know…
Table of Contents
Things to consider when buying polycarbonate
Colours – there is a range to choose from
Additional UV protection
Condensation protection
R-values explained
Styles of polycarbonate sheet
Polycarbonate greenhouse


Things to consider when choosing polycarbonate

  • Find a reputable supplier – some offer long guarantees of 10 to 15 years.
  • Are you looking to add some colour to your garden?
  • Do you need extra protection, such as against UV light or condensation?
  • Maybe the climate where you live calls for additional insulation.
  • There are a range of styles on offer, each with their own particular benefits, explained below.

Coloured polycarbonate sheet 

Multicolour polycarbonatePolycarbonate is available in a range of colours, which determine the light transmission of the structure; the more light entering the greenhouse, the warmer it will be. Common choices for greenhouses are clear, bronze and white, which is sometimes referred to as opal. Clear polycarbonate sheet allows the most light to pass through; this is generally the best option for more northerly latitudes. Bronze and white polycarbonates reduce light transmission by about 50 per cent, which can be beneficial in warmer climates, or for growing more sensitive plants.


Additional UV protection

All polycarbonate offers protection against UV rays. However, weathering, which can also cause the product to become discoloured, can reduce this protection. Some suppliers offer polycarbonate with additional protection against weathering and UV rays to increase the lifespan of the product for outdoor use.

Condensation protection

Some suppliers offer additional protection against condensation, as this can reduce light transmission within a greenhouse and decrease productivity.


Gardeners living in northerly latitudes could save in the long term by investing in twin- or multi-wall polycarbonate. The increased insulation will reduce winter heating costs and provide long-term savings.
Those living in warmer areas may also benefit from additional insulation to protect plants from the damaging effects of too much heat, and to increase diffusion of light, which is reported to increase plant productivity.

R-values explained

The R-value is a measurement of the effectiveness of the insulation offered by the polycarbonate sheet – the higher the number, the higher the level of insulation. A high level of insulation ensures that temperatures will not rise too high in the summer, or drop too low in the winter.

Styles of polycarbonate


Single-layer polycarbonate sheet

Single layer polycarbonateSingle-layer polycarbonate sheet provides the highest level of light transmission but little insulation and no diffusion of light. It is an attractive choice as it provides the clarity of glass, but has the added benefit of being much stronger, more durable and lightweight. Uneven distribution of light due to the lack of light diffusion can negatively impact plant growth by creating hot spots within a greenhouse. Due to the lack of insulation,
single-layer polycarbonate may not be warm enough for year-round use
in greenhouses in most areas, but it can work well in a cold frame.


Corrugated polycarbonate sheet

Corrugated polycarbonateCorrugated polycarbonate sheet has a stronger structure and requires less support than other types of polycarbonate; this can reduce the amount of framing required and reduce installation costs. A corrugated pane increases light diffusion within a greenhouse to give a more even distribution of light. But as it is a single-layer structure, it provides poor thermal insulation.
When used for roofing the lack of thermal insulation becomes an
advantage, as the heat lost through the roof during winter can prevent
snow from accumulating and blocking the light.

Twin-wall polycarbonate sheet

Twin-wall polycarbonateTwin-wall polycarbonate sheet works in the same way as double-glazed glass; it provides greater insulation and protection from direct sunlight than single sheets of polycarbonate, which can be beneficial for more sensitive plants. The thicker the sheet of polycarbonate the greater the level of insulation provided: 4mm twin-wall polycarbonate has an R-value of 1.43; 6mm twin-wall polycarbonate has an R-value of 1.54; and 10mm twin-wall polycarbonate has an R-value of 1.89, double that of single pane glass.
This may prove to be more cost effective than single sheets in areas with a long and cold winter season during which greenhouses will require additional heating.
Double layers diffuse the light entering the greenhouse structure resulting in a more even distribution of light and heat. When light is diffused it is distributed throughout the greenhouse more evenly. This reduces the intensity of the light reaching the plants inside as well as reducing the incidence of hot and cool patches within the greenhouse. Research shows that even distribution of light can help to prevent plant injury such as leaf burn; it can also provide benefits such as improved crop yield, higher leaf count and a shorter crop time.

Multi-wall polycarbonate sheet

Multi-layer polycarbonateMulti-wall polycarbonate sheet has all the properties of twin-wall polycarbonate but provides a greater level of insulation, which increases
the more layers are added. Up to six-wall polycarbonate is available from some suppliers. The more layers used, the greater the level of insulation
will be. Although multi-wall polycarbonate requires a greater initial investment than single or twin-wall, the increased insulation provided can result in long-term savings on winter heating costs.

Sample R-values for different thicknesses of polycarbonate sheet
(Exact values may vary between manufacturers)
Type of greenhouse pane R value
3mm single glass 0.95
Single-layer polycarbonate 0.83
4mm twin-wall polycarbonate 1.43
6mm twin-wall polycarbonate 1.54
10mm twin-wall polycarbonate 1.89
16mm triple-wall polycarbonate 2.50
Five-wall polycarbonate 3.03