Polypropylene (PP) is in many respects similar to high-density polyethylene. However, instead of forming a long polymer chain made up of repeating –CH2-components, the polypropylene molecule has a series of CH3 groups that hang off the main carbon backbone. Porex’s PPs are considered isotactic PPs, with the CH3 groups oriented on one side of the carbon backbone. This orientation creates a greater degree of cystallinity, making PP stiffer and more resistant to creep (the tendency to flow under stress) compared to PE.

Available in molded shapes, sheets and tubes, the nominal pore size for PP ranges from 80 to 150 micrometers. PP is highly resistant to most acids and alkalies and is resistant to most organic solvents below 176°F (80°C). When not stressed, PP may be used at temperatures ranging from 200°F to 300°F (93°C to 149°C). Further, PP can normally be subjected to steam sterilization.