We get a lot of questions about polycarbonate as a greenhouse covering.
For the most part we find that people are trying to over complicate the issue.
This article will address just what greenhouse polycarbonate is.
Polycarbonate, simply put, is a plastic.
It is lightweight (1/6th the weight of glass), virtually unbreakable (impact strength 200 times greater than glass), has excellent weather resistance (due to the UV protection on one or two sides of the sheets), has excellent insulation (due to the multiple layers with channels in between) and is flexible and easy to install (see specific information on each thickness).
You can purchase it in solid sheets, corrugated, or multiwall.
The typical configurations used for greenhouse glazing are corrugated and multiwall.
The reason the solid sheets are not recommended is due to the fact that they are not widely available with a UV protection on one side.
The UV protection will keep the sheets from yellowing or getting brittle.
Some people will mistakenly think this affects the light transmission of the sheets.
It has nothing to do with that.
The sheets with UV protection on one side are typically guaranteed for 10 years against yellowing and hail damage.
This will vary from manufacturer to manufacturer.
There are also sheets available with UV protection on both sides.
These are typically used for vertical applications such as fencing where both sides of the sheet are exposed to the sun.
While this may be used for a greenhouse it is typically more expensive and unnecessary.
Corrugated sheets are a single polycarbonate that is typically very thin, usually 0.
8mm.
It is available in a wavy or greca style.
It will work great for a greenhouse, but will not have as much insulating factor as a twin wall sheet.
The easiest way to visualize a twin wall sheet is to think about looking down the edge of a cardboard box.
There is a sheet on the inside, a sheet on the outside with a rib running in between the sheets.
The rib in a cardboard box will be wavy.
The rib in polycarbonate runs straight between the 2 sheets.
Both sides of the sheet are flat.
The sheets are clear, but not "crystal clear" like glass.
The rib will distort your view somewhat.
It is available in 6mm, 8mm, 10mm and 16mm thickness.
The 16mm is typically a triple wall - meaning there will be a sheet running between the 2 exterior sheets.
There are also some 8mm sheets available as a triple wall.
Typically, the thicker the sheet, the better the insulation factor.
One should consider the initial cost of the polycarbonate when considering the overall savings due to energy costs.
A 16mm sheet is about 5/8" thick.
Polycarbonate sheets are shipped by truck line because they cannot be rolled and must be shipped flat.
Most greenhouses are glazed with clear polycarbonate.
It is available also in bronze and opal.
These will cut down on light transmission drastically.
Of course, whether you want to consider opal or bronze will depend on the needs of your particular plants.
There are also some specialty sheets available which will cut down on the heat buildup in the greenhouse.
Two such examples are Polycoolite by Polygal and GE Lexan Thermoclear Plus Softlite.
In closing, polycarbonate is an excellent choice for greenhouse glazing.
It is easy to install and durable.