Classification of defective plastics as waste allows waste treatment while input tax credit need not be varied. Defective printed plastic sheets and pouches arising from misprinting, improper lamination and sealing/trimming that are unfit for their intended use qualify as waste, parings and scrap of plastics under Heading 39.15. Assessing officers must verify the true nature of such waste to prevent misuse. Pursuant to the relevant credit-adjustment provision, input credit already taken need not be varied merely because inputs are contained in waste arising in the course of manufacture, regardless of clearance on payment of duty.