Everything You Wanted To Know About The “Greenhouse Plastic”

Redwood Plastics is the plastics distributor who runs this website and one of our most common inquiries is “Hi, I’m looking for the plastic for a greenhouse…” what ends up happening is an educational process, often via email, whereas the options are narrowed down to really your only option: twin-wall polycarbonate. The most common misconception people have is that regular acrylic or polycarbonate (the smooth stuff) is a good option: it isn’t. For one, you’ll be paying a lot more, but more importantly, the R-Value (heat insulation value) and weathering resistance will be much poorer. Acrylic has decent UV-resistance but regular unmodified polycarbonate has poor weathering including from the sun. Both options will be much more pricey than the twin-wall, which you should have been using in the first place.

Twin-wall polycarbonate has excellent R-values and resistance to UV-light and weathering. The 4′ x 10′ x 6mm profile is what we be considered “standard”. Many customers do specify 8mm or even 10mm thick polycarbonate and we often wonder why. Yes, the R-value would increase; however, you lose light transmission value. So are you really ahead? Certainly you are NOT ahead when it comes to price as 8-10mm thick polycarbonate is much more expensive. We’ve had members of the “DIY” community have excellent results with 6mm thick twin-wall in Saskatchewan where winters can reach -30 degrees Celsius. For more information on the tradeoffs between different polycarbonate thickness options, click here.

The benefits of twin-wall polycarbonate are excellent and they include:

-Ease of fabrication via common woodworking tools. Diamond/carbide-tipped blades not required.

-Relatively low price

-Full UV-stabilization/resistance to weathering

-High light transmission

-A product that is meant to be for greenhouse applications!

For a personal response to your questions on twin-wall polycarbonate, contact Redwood Plastics today.

 

 

Multi-Wall Polycarbonate – Beware Tradeoffs

When it comes to multi-wall polycarbonate, demand outstrips supply. Meaning demand for sheet sizes and profiles outside of the 4′ x 10′ x 6mm (1/4″ nominal) standard. Multi-wall polycarbonate is an excellent plastic for several home projects. The standard sheets are relatively cheap in comparison to other industrial plastics. Unlike standard polycarbonate, multi-wall comes UV-stabilized for outdoor use and can be easily fabricated using household tools. It does not require special hardware – any screw with a washer affixes it just fine.

The problem we see as a plastic distributor is demand for non-standard thicknesses and sizes, most commonly 16mm or 8mm thick material. What you need to realize is those profiles are much rarer and the increase in cost will not be proportional to the increase in sheet thickness. What you also might not realize is the tradeoff you make in properties, not simply in cost.

For example, while there is slight variance among manufacturers, for the most part the properties are very similar. Take these two as an example:

6mm thick twin-wall polycarbonate:

R-value 1.6
Light transmission: 85%

10mm thick twin-wall polycarbonate:

R-value 1.9
Light transmission: 75%*

*In the often requested 16mm multi-wall, light transmission drops to around 64%

Note that by adding 40% to the thickness of the material you gain only 15% R-value (thermal insulation) yet you lose 10% light transmission. In the case of a greenhouse application that 10% can have an effect on plant growth.

The point of all this is to have a clear picture of the cost and consequences of going with thicker multi-wall polycarbonate. It is still an excellent product, but it comes down to a tradeoff you need to be aware of – increased thermal insulation in exchange for increased price and less light transmission.

Any questions? Contact us.