If you are looking for a light escape cord, you might consider one of the high tech Technora core cords like New England Tech Cord. The one in the link is 5mm. I have some 3mm, but I haven't been able to find a source in a while.

FWIW, I hear knots (or any sharp bends) are a significant weak point with these cords and they are much weaker at a knot than their rated working load. It also sounds like they wouldn't take well to repeated use.

Make sure you research any solution you plan to use.

-john