Definition: A greenhouse needs to have excellent insulation or your plants won't survive. The R value is a commercial measurement developed to compare the thermal insulation of different greenhouse siding materials. The larger the number, the better the insulation and the more efficiently your greenhouse will both heat and cool.
The ratings can sometimes be a bit subjective, but they do provide a practical means of comparing different materials
Alternate Spellings: R-value
Examples:
A single pane of glass has an r-value of .95, where a double pane would increase the r-value to a 2.0 and make the greenhouse twice as efficient.
