Many collectors do not accept envelopes with paper waste because of the glue. Glue can clog the remanufacturing process, but some councils take the view that asking householders not to include them will put them off recycling, so they accept them, but it ie best not to include them. Some recyclers do not accept window envelopes, but some can cope with these.

You may therefore find you are limited to re-using them, by buying stick on labels, or composting them.

Window envelopes are only compostible if you either remove the plastic window , or if the window is made from cellophane.

Jiffy bags are made up of many materials, and so long as this doesn't include plastic they can be composted.