EMS Jomar used to sell a very good polyurethane coated kevlar cable but unfortunately it is not available anymore.

Currently I use the vinyl-coated kevlar cables (kev-cord) from ACP Composites http://www.acp-composites.com/acp-cord.htm The 0.038" size is good for up to 120 sized planes, while the 0.058" size is good up to 40% GS planes. This is the same cables being sold by Don's Hobbies. The vinyl coating protects the kevlar from UV rays (which damages it in the long run) but I noticed that it can peel off with hard chaffing, so try to minimize any rubbing if possible.

Hope this helps