Urethane tends to be very sticky and could potentially clog sintered vent pores very quickly. Some customers have had success using sintered vents with molding Urethane, and some other customers have not had success molding Urethane using sintered vents. Furthermore, not all Urethanes are made equal and some grades could clog a sintered vent faster than other grades. As a general rule we do not recommend using sintered vents with molding Urethane due to the gases and residues emitted. Instead we recommend that you machine a custom vent in the mold at the end of the flow front.