Static Dyneema 5.5mm diameter cord that is almost as strong (1800 daN kg) as 9mm rope. Sold by the metre.
Use it for restringing nuts etc to save weight and bulk (it is only 20g/m), but tie a Triple Fisherman's Knot rather than a double fisherman's knot (if you don't know the difference then ring us up and we'll explain!), and also you must cut it with a hot knife, pull the sheath back 5mm, chop this amount from the core, pull the sheath over the end of the core and heat seal it in place - you need to do this because the core and sheath do not bond together when cut.
Please note: It is NOT suitable for Prussik Loops (it's too stiff and slippery and melts at too low a temperature, 145ºC, as opposed to 215ºC for nylon). It is also not suitable for abseiling as there is too much sheath slippage (and it may melt!).
NB: The best lengths for restringing Hexes and other nuts is 1.1m and for cams 0.75m - please see below.