This ProVantage Glass Block Channel is constructed of rigid white vinyl. It is available in 4″ thickness for use with almost all glass block options. The Provantage Channel is pre-drilled for easy installation and it is sold in lengths of 40″ or 72″. The ProVantage Horizontal Spacers is used in Silicone installations. It’s used horizontally between glass blocks to create separation for even joints in a silicone glass block installation.