Inflating two layers of poly with air helps with insulation.

It will also help poly to last longer due to less rippling and flapping in the wind.

B&W typically supplies our customers with AT Plastics poly.

Ask for "Thermax" anti-condensate thermal poly for your inside layer of poly, and "Super 4" clear 6 mil poly for the outside layer.

For double layers of poly on your greenhouse you would inflate the two layers using an inflation kit, which includes a blower motor.

R values for energy conservation.

“R-value” is a commonly used term to measure a material’s energy conserving (or insulating) properties. It is a measure of resistance that a material has to the flow of heat. The below R-values reflect real world outdoor situations. Specific brand-name products may vary from these figures. It is always good to check on the stated R-value of a product as you evaluate a glazing. Also, consider other important attributes when evaluating glazings or insulation materials.

The more energy conserving a material is, the higher it’s R-value.
note: The term R-value is a common measure of insulation(hrºFsq.ft/BTU)
R-Value
Polycarbonate 16 mm triple wall 2.5
Polycarbonate 8 mm triple wall 2.0-2.1
Polycarbonate 8 mm double wall 1.72
Acrylic double wall 1.82
Glass double layer 1.5-2.0
Glass double layer low-e 2.5
Glass triple layer 1/4” air space 2.13
Fiberglass glazing single layer 0.83
Polyethylene double 5 mil film 1.5
Polyethylene double 6 mil film 1.7
Polyethylene single film 0.87
6 inches of fiberglass bat insulation 19.0
Polystyrene (styrofoam) 1” thick 4.0

Note: You may also find products sold with a U-value instead of an R-value. A U-value is the inverse of an R-value. To convert a U-value to an R-value do the following: 1 divided by the U-value equals the R-value. For example: fiberglass has a U-value of 1.2 when it is divided into 1 it equals a 0.83 R-value.

U-Value or overall heat loss

BTU per square foot per degree F. per hour.

Factors of various greenhouse Coverings
U-value
Glass, single layer 1.1
Glass, double layer (1/4” space) 0.7
Glass, triple layer (1/4” space) 0.5
Polyethylene, single layer 1.1
Polyethylene, double layer 0.7
Double Acrylic or polycarbonate 0.6
Corrugated Polycarbonate 1.2
Concrete Block 0.5
Plywood 1/2” thick 0.7
Concrete poured 6” 0.8
Concrete Block or plywood plus 1” foamed urethane 0.1
Concrete Block or plywood plus 1” polystyrene bead 0.2
Greenhouse with thin thermal curtain 0.3 to 0.7
Uninsulated Perimeter 0.8
Insulated Perimeter 0.4