Constructed of high density fine Star prene fibres with flagged ends to hold water and cleaning solutions for easier washing. Will fit all Extend-A-Brush handles. Will not scratch plastic windows. Star prene is a lightweight polymer fibre that does not stain, discolour or become brittle. It resists most cleaning chemicals and withstands heat up to 200°F. This space age material will not rot, mildew or absorb odors.