Will polyurethane collapse after several years?

Typically, when installed according to the manufacturer’s instructions and the requirements of CAN / ULC-S705.2 (Standard for Thermal Insulation Spray Applied Rigid Polyurethane Foam, Medium Density – Application), and having fully matured and completed its curing, polyurethane spray foam will not sag because it strongly adheres to the surfaces against which it is applied.