Ok, maybe it was too hard… promise the next one will be easier!
people were close when they said sticky tape but it was in fact:
Not sticky packing tape, but the textured plastic kind people use to bind cardboard boxes closed. The characteristic sound was created by putting a contact mic on the tape as I split it, lengthwise..
one more listen:
(the fact I used a contact mic rather than a ‘normal’ mic probably didnt help, but hey! more than a few of the msot interesting sounds in my library were captured via it)