When the material is cooled down, new cross-links are established, which bond the elastic blocks into rigid three-dimensional networks. This means that TPEs show elastic properties that are similar to those of elastomers, while allowing for repeat deformation and recovery as known from thermoplastics. Thermoplastic elastomers are thus free flowing and formable. TPEs have a block structure (A-B-A), typically with thermoplastic end blocks (A) and an elastic midblock (B), placing TPEs midway between thermoplastics and elastomers. ISO/EN/DIN 18064 furthermore classifies the wide variety of TPEs in 7 classes: TPA, TPC, TPO, TPS, TPU, TPV and TPZ. The 3rd letter designates the respective subclass: A for Amide, C for Copolyester, O for Olefin, S for Styrene, U for Urethane, V for Vulcanisate, and Z for various other materials.