4 Best Plastics for Greenhouses
Polyethylene
This is the most common plastic used for greenhouses. It’s thin (6- to 12-mil), durable and the least expensive of the four greenhouse plastics. A single layer of polyethylene works well, but a double layer is ideal.
“Blowing air between layers creates an air pocket that acts as insulation,” says DeVore. “With a double layer, there’s a lot more efficiency in trapping sunlight and heat.” Also, more condensation occurs with a single layer of plastic than a double layer.
Polyethylene can only cover wood or metal frames. “It destroys a PVC (polyvinyl chloride) frame, so if you must use PVC under polyethylene, brush a protective layer of paint over the PVC,” DeVore says.
Polycarbonate
This common plastic is more expensive than polyethylene. “There is better light transmission with polycarbonate than polyethylene, so this is a consideration if you worry you will not get enough natural sunlight in your greenhouse,” says DeVore.
Because polycarbonate is rigid, it’s used for end walls and to create rooms in a greenhouse. “Polycarbonate lasts 10 years or so versus two to seven years for polyethylene,” says DeVore. The drawback? You can’t use it to cover domed or arched greenhouses.
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