Delrin can be found in some local plastics supply shops - Plastics sources
From: Xodiac
Subject: Re: FL: Tails in motion….
Mobile tails can be done in two ways that I know of, and there’s probably a few others as well as variations on these.
The first is the method I am currently using, and I know others have done this as well. Basically, take a delrin rod – obtainable at a good plastics supplier – and use a paint-stripping gun to heat the stuff up. It can be shaped very nicely when heated above 1000 degrees or so, and you can put a pretty nice curve into it. Wrap some foam around it, then wrap your fur or whatever around the foam, and you’ve got a tail that is very flexible. You may need to add some fishing weights along the tail; then again, you may not. Depends on how mobile you want it and how much your fam restricts its movement (or acts as a weight in itself and helps the movement). Attaching it to the costume may be tricky; in my case it’s made easier by how the costume requires a backback type of arrangement, and I just attached it to that.
According to Diadexxus, on shaping delrin for tails and other things;
3/4” is the perfect size of the rod. You heat it up (heat gun) until shiny/soft to have the shape you want, then let it naturally cool down (dont try to speed it up with water, it will shatter) and it keeps that shape. Be sure to use two sets of pliers to bend the rod into position until cool. That plus wear gloves while doing this, as the plastic stays extremely hot for quite some time. Add a loop at the end and you have room for your belt.
Here’s two shots of the delrin understructure; [ Ziptied tail ] [ Hooked up to me via belt ]