The skim fraction that is a by-product of centrifuging process , has 3%-4% rubber content .such a low percentage plus an increased proportion of non rubber constituents demand that to recover the rubber ,a very strong acid be used .This grade ,though not technically good,is still vary viable economically and is used in non critical application .The coagulated rubber is thoroughly washed with water and creped by passing through roller the sheet obtained is dried and is marketed as skim crepe.