String? As in the string you will be drawing? I would suggest Dacron. That's the material most bows use to start off with. I wouldn't know if it's perfectly suitable though. My suggestion is to mail an Archery Store and ask them what they would suggest. I use a material called Fast Flight but that might be too fast and cause the bow to break. Dacron is the typical material people start off with (target archery and take down bows).