How do I fix frayed nylon on the collar?

How do I fix frayed nylon on the collar?

I have two Patagonia items (Nano Puff jacket and a Nano Puff vest) that both have frayed collars, probably from rubbing against beard stubble. The nylon material has worn through exposing the fill material in the collar. The rest of the garments are in great shape, so I'd like to fix. Any suggestions?