C.R. LAURENCE SR38B CRL 3/8" Sof Rod - 3600" Case. CRL Sofr Rod is a state-of-the-art sealant backing material combining the best properties of both open and closed cell backer rods in a single, trouble-free product. Sofr Rod is a continuous length of extruded polyolefin foam made with a non-absorbent outer "skin" and a highly resilient interior network of open and closed cells. Sofr Rod will not out-gas if ruptured. It can be used in temperatures ranging from -45 to 160 F (-43 to 71 C)..