Thin skin is a thin plastic film from Wapsi, printed with different colours and patterns.
It is stretchable enabling good tie in and secure holding.
The backing makes it easier to cut to shape before peeling off to leave you with a transparent material with or without patterning with a shiny side and matt the other to vary your pattern again.
Thin skin is 0.004" thick and can be used on flies past #18. Uses include nymphs, wingcasses, scud backs, sowbugs, crayfish and saltwater shrimps.
You can use if for downwings like caddis flies as the Oak and Bustard pattern give a lovely natural effect sedge wing.