Gamma makes a 18g string called Power Play that is a kevlar string. I stumbled onto it, and played it a couple of years. It is extremely low power, but once i got used to it, I played well. It is not arm friendly, but my elbow handled it better than poly. It does continue to lose tension over time, but it is gradual. It lasted forever for me... the string would look like it was about to break, and still last another week or two. I think it is about $7 a set, so you can check it out.