Q: Can GRS certification cover zipper sliders and teeth?
GRS applies to textile products and to the recycled content in them. Metal sliders, pulls and stops are not textile, so they normally fall outside the certified content and must be identified separately in the product description. The standard allows non-textile parts to be excluded from the recycled content calculation, provided they are declared and do not undermine the claim.
In practice a GRS zipper is usually a recycled polyester tape with conventional metal or polymer hardware. The transaction certificate will describe the tape and its recycled percentage, and the hardware is listed as a non-certified component. If you want a recycled claim on the slider itself, that requires a different scheme and a different chain of custody, and the claim must be worded so it does not imply that the whole zipper is certified.
Ask the supplier for the product description in the scope certificate, the bill of materials showing which parts carry recycled content, and the transaction certificate for the shipment. Marketing text should follow that wording exactly, because overstating the certified portion is the most common cause of a rejected claim.