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Injection moulding, the predominant production method used in Canada, involves injecting PVC, PU or molten rubber into a mould, which is fitted to the lasted upper. PVC is used in low-priced boots. PU soles can be injected to form single- or double-density soles. The production of double-density soles involves the injection of two densities of PU. The denser PU is injected first to form the outer sole and then the less dense PU is injected to form a softer midsole. Also, some producers manufacture leather safety footwear with double-density PU soles that have rubber or thermoplastic inserts in their outer soles. This is accomplished by placing metal inserts in the injection moulds to provide space into which the rubber or thermoplastic inserts can be placed. Once the leather safety footwear is removed from the mould, excess injection material is trimmed from the sole area, and the footwear is sent for finishing and packing .
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