Thanks for your post. I have learned that there now is an extremely strong, relatively thin line available through climbing sources such as www.rei.com that would be an excellent choice. I believe it is a new product. It is called Spectra line and is available in a thin, 5.5mm, diameter with a 17.6+ kilonewton breaking strength. That's a measured breaking strength well in excess of typical bulky climbing ropes which often measure at around 10 kN (note, spectra lacks the elasticity of a "dynamic" climbing rope, so it would not be suitable to catch a falling climber, but is fine for rappelling). It's a bit pricy at $1.05 per foot, but is considerably stronger than the other lines discussed such as perlon, paracord, etc. Suitable perlon could be had at about a third of that cost. Anyone interested should look into the knotability of Spectra which is more slippery and would require special care when choosing and tieing knots.<br><br>