You need a webbing 'closed' sling: do you go for Spectra, Dyneema or nylon? Well, it depends! Spectra (made by Honeywell) and Dyneema (made by DSM) are brand names for the same thing - HMWP - High Molecular Weight Polyethylene.
HMWP is twice the strength of nylon for the same weight meaning you can get equally strong slings with less material. eg the Aspiring 300 mm closed sling sold by Treetools for the Trango Cinch set-up and/or custom rope savers is 15 mm Dyneema - if that was nylon it would have to be 25 mm for the same strength. The downside of Spectra and Dyneema is that it has a low melting point when used as a prussic.
If the prussic is static (like the rope saver) then this is not a problem. Treetools find Spectra and Dyneema is preferred for slings used in personal climbing set-ups and the larger nylon closed slings for rigging etc. You will also pay more for Spectra or Dyneema.
