Is there a general ratio on how the total length of backing compares from dacron to poly type backing, assuming the same breaking weight for each? For instance, if I have a half inch of 20lb backing on my reel, how would I know how much more length I could get if I switched it over to a 20 lb poly, gel spun or that type of material for backing and still fill it up to the 1/2 inch level? I'm sure there is some variation in the diameters of some of the poly backings, but can anyone get me into an approximate ratio? Thanks.