Major Type and Grade Selection

A number of traditional factors are often specified for polyurethanes, such as hardness and tensile strength, that do not control the final performance properties. 

The hardness of polyurethanes can be obtained by either the density of the hard segments, the choice of curative, or the addition of plasticizer. The importance of hardness is to control the rigidity of the part (if not reinforced) or its softness to conform to the shape of some other object it passes over. For very low hardness ( 60 A) applications such as rolls, TDI esters are the most suited, whereas ether-based materials are least suited. Hard materials do have better abrasive resistance than soft materials. 

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