Polypropylene is a polymer of ethylene with an isotactic arrangement of methyl groups. The material has a partly crystalline structure. A high rigidity can be achieved by stretching processes. The melting point is low which results in good thermal processing and welding properties. This material has the lowest density of all polymers – it is lighter than water and thus floats easily. It does not absorb moisture and has a good resistance against acids and alkalis. A low electro-static charge absorption is another advantage in its use. Using various additives further material properties can be achieved. The sun’s rays lead to disintegration. Recycling can be done thermically.