I've posted this before, so I apologize for the redundancy...
There are only 3 basic types of modern bowstring materials (not counting primitive materials like natural fibers, silk, linen, hide, etc.).
Within their specific categories, the characteristics don't vary a lot. The higher grades will have less stretch/creep, but they are still made from the same basic materials.
#1. Polyester - Or, as most of us like to call it, "dacron" (which is a trade name that has expired). For now we have B-55 and B-50. B-55 is a slightly higher grade so it has a little less stretch and creep and a tad more durability, but it has the same basic characteristics as B-50.
#2. HMPE - High Modulus Polyethylene, aka Ultra High Molecular Weight Polyethylene (UHMWPE, UHMWP). Basically a very strong plastic fiber--the strongest man-made fiber available. Trade names include Spectra and Dyneema. Bowstring materials include 652 Spectra, Dynaflight '97, 8125, Mercury, etc. Very strong, almost no elasticity, low creep. The first bow string material in this category was invented by Ray Browne and Bob Destin, the original "Fast Flight".
#3. HMPE/LCP (Liquid Crystal Polymer) Blends - LCP's include the brand names "Vectra" and "Vectran". Very temperature resistant, practically no stretch or creep, this type of yarn was incorporated with HMPE to create the most stable (in all temperatures) of bowstring materials. These include Trophy, 450+, 452X, BCY-X. This material was first developed into bowstring by Bob Destin of BCY. As a side note, there are no 100% LCP bowstring materials because it won't withstand flexing in one point (like the nock point) over and over. Like the old Kevlar material, if it were 100% LCP it would break, usually without warning.
Anyhow...that's the break down. Most variations you see (or hear) within one of these three categories is normally going to be much more due to the string build, bow design, tuning, nock fit, arrow weight, your release, etc.