This durable co-poly string is very, very spin friendly. The slick surface of RPM Blast allows the main strings to slide out of alignment, grab the ball and then snap back to add spin to the shot. While all co-poly monofilaments do this to some extent, our lab tests confirm that RPM Blast is exceptional in this regard. Though RPM Blast offers a slightly softer feel than traditional polyesters, it is by no means the softest co-poly available. It is an ideal choice for big hitters with heavier racquets seeking maximum control, durability, and spin. (And it seems to be working quite well for Rafa!)