A low density, open cell SPF weighing 0.4 to 0.6 lbs. per cubic ft. when fully cured. It is spray applied to a substrate as a liquid and expands approximately 100-150 times its original volume to form a semirigid or flexible, non-structural SPF insulation. 1/2 lb. Foam-LokTM has an R-value of 3.5 per inch.