Polybushes are a polyurethane replacement for the standard rubber bush. Its properties are stiffer then rubber and allow less flex. They are also less susceptible to heat, meaning that the bush is mounted near the engine, exhaust or brakes that they will stay firm rather than becoming soft like a standard rubber bush.
Apply some washing up liquid to the outside of the bush to ease fitting. Press the polyurethane bush into the lollipop mount at an angle so one part of the lip is already in the bore of the mount, when the bush is then pushed in the rest of the lip will follow. Make sure the lip has fully popped out the other side of the arm.
*Images are for illustration purposes only, what you receive may vary slightly in colour due to stocking*