Flexible polyurethanes are open-celled polyurethanes with limited flexibility and re-shaping feature. It is popularly known as sponge with its wide-spread use. Low density sponges (13-40 kg/m³) are produced in continuous lines with slabstock technology, high density foams (40-80 kg/m³) are produced by molding method. In applications made with the molding method, the liquid polyol system and isocyanate are injected into the mold with the help of a machine. The foam formed as a result of the reaction takes the shape of the mold and becomes flexible. Generally used isocyanates are prepolymers and they are TDI or MDI based. If the prepared polyol systems are not used with the recommended isocyanates, technical problems arise or sponges with the desired physical properties cannot be obtained.
At thesame time, semi-flexible or very flexible viscoelastic (memory-foam) sponges falls into this group. Today, depending on the developing technology and needs, it is possible to produce foam with the desired elasticity, hardness and density.
