A shell type fitting cover provided and is formed from a polymer material or a flexible thermoplastic sheet. A continuous gasket is affixed to the peripheral edges of the shell fitting prior to its installation. Preferably the gasket is a flexible, compressible material. The fitting includes a shell having two ends that overlap onto the linear portions of a pipe insulation system and a longitudinal seam that allows the shell to be installed over an existing piping system. A strip of foam gasket material is provided along each of the peripheral edges in order to create a seal where the installed fitting overlaps the linear sections of insulation as well as where the fitting shell overlaps itself at the longitudinal joint.