How much does HDPE sheet expand and contract?

Indoor applications experience little to no expansion as the temperature is constant. For outdoor ambient temperature applications, the rule of thumb is that a 4 x 8 sheet will expand as much as 1/2" in length from a hot summer day to sub-zero winter temperatures in cold climates. HDPE sheet expands more in length than in width, due to its molecular structure.

The easiest formula to use for an exact expansion / contraction dimension is as follows:
Degrees Fahrenheit:
0.00011 x degree variance(°F) x length in inches
Example: 0.00011 x 30°F temperature change x 96" long sheet = 0.3168" or approximately 5/16"

Degrees Celsius:
0.00019 x degree variance(°C) x length in inches
Example: 0.0001 x 16.7°F temperature change x 96" long sheet = 0.3173" or approximately 5/16".

While these numbers may seem high, expansion can be easily negated by using correct installation techniques.