There's still some Rainys' nymph foam in one of the materials boxes, even though haven't tied many nymphs lately. It's used to form an underbody by wrapping it up & down the hook, thereby making the body wider &/or fuller like the double wire nymph hooks shaped like triangles. Also comes in handy to make a floating nymph suspend just off the bottom with split shot, but it has to be waterproofed with tying cement to get it to float for any length of time. Can also use it under some dry fly patterns !