Looking to replace the main halyard on Paradigm 2, any thoughts on material and thickness welcomed
Does the mast have a ClamCleat or a wrap-around cleat (see pictures below)? If it has a ClamCleat then you need a low stretch halyard with a sheath. Low stretch rope is really important as any stretch results in the mainsail pullingt down the mast when you pull the cunningham on. I use Marlow Excel Racing GP 78 4mm Halyard / Control Line, Dinghy Yacht Dyneema Rope. If you have a wrap around cleat then you can use 4mm dyneema without a sheath.
(https://www.pinbax.com/images/micro-racing-p5347-8303_thumb.jpg) (https://www.pinbax.com/images/open-jam-halyard-cleat-length-62mm-p9877-18869_thumb.jpg)
No cleats used, soft loop on current halyard goes onto a tooth rack.
Ah in which case, I'd eaither recommend dyneema - and splice in a loop or change the rack for a wrap-around cleat