Hareline flashback is a great durable synthetic material that is often used to make wing cases on nymphs, can be wrapped to form a body, or just laid over the back of a pattern to form a scud like back.  Because of the nature of this material and the amount of colors it’s available in there is a lot of room for customization.  
Uses: Wing Cases, Scud backs, making bodies on nymphs
Comparison: Similar to Sili skin, but in a narrower wrapped sheet, and coming in different colors.
Example Flies: GTI caddis, Flashback Pheasant Tail, Rainbow Warrior,