CRL Thermoplastic Rubber (TPR) Setting Blocks are compatible with almost anything, meaning you can use them in designs calling for the use of modern structural glazing sealants. They are formed of a 90 durometer shore hardness thermoplastic rubber that performs as well as traditional neoprene setting blocks. They are available in the most popular sizes of neoprene blocks. They have excellent chemical resistance, and do not mar or stain surfaces. Job specific testing prior to start up is recommended with each silicone sealant manufacturer. Important Notes: To ensure sealant to block compatibility, the manufacturer of the silicone sealant can test the compatibility of job site representative accessory materials with their silicone sealants using ASTM C1087-87. Results of the compatibility test will be forwarded in writing. Testing takes approximately four weeks from receipt of samples.