Exemption for glass fibre inputs reduces additional duty for manufacture of pollution-control goods, subject to certification and repayment on noncompliance. Exemption removes additional customs duty in excess of a specified ad valorem rate on imported glass fibre sewing thread and glass fibre filter cloth under Heading 70.19 when imported for manufacture of goods intended for pollution control. The relief is subject to an importer's undertaking, production of a certification from a senior environmental officer within three months (or extended period) confirming the end-use, and payment on demand of the duty difference if conditions are not met.