Abstract Glass fibre reinforced composite pipes were fabricated by using an IPN blend of 0%, 10%, 20%, 30%, 40%, 50% PU prepolymer (Polyurethane) with VER(Vinylester) resin. The prepared IPN (Interpenetrating polymer networks) composite pipes were subjected to boiling water immersion tests in order to study the effect of moisture absorption characteristics. The Burst strength and Hoop strength of water immersed specimens were evaluated (3, 6, 9, 12 months) and compared along with dry composite specimens. It was found that, percentage of moisture uptake was significantly reduced with increase in PU loading into the IPN system as well the Burst strength and Hoop strength of the specimens were found to be diminishing with raise in percentage of moisture uptake and raise in temperature; contrarily, the addition of PU significantly reduced the moisture intake, in addition to that the PU added IPN pipe offers better mechanical strength while compared with neat Vinylester pipes.