Calculation of insulation thickness can be complex given the number of variables, include operating temperature, wind speed and dewpoint. ISO-C1 polyisocyanurate insulation, for instance, offers higher insulation values (R-factor) for lower temperatures.

Thickness calculations should generally be done or approved by qualified engineers. Industry-standard software (3-E Plus) is available free from the North American Insulation Manufacturers Association.

See Insulation Panel Thickness for polyiso structural insulated panels.