While agreeing that chafe is the leading cause of mooring line failures and indeed, most line failures, I'd be highly interested in any study that has shown either heat or a lack of water lubrication is a major cause of line failure.
You can place chafing gear over the potential wear spots on your mooring lines or your dock lines and rest easy that you'll be doing far more to keep them from chafing and parting than any risk from heat might concern you. The chafing gear can be any number of materials including canvas, leather, or garden hose in my case.
Dacron is the most abrasion resistant of line materials and has less stretch than nylon with nearly the strength. I'd recommend a construction like Pli-moor which is similar to Brait and other braided lines. Note that these are not 2-in-1 braided lines which have a core and a cover but the ones where the actual strands of the line are braided. 2-in-1, or double braid, is not as abrasion resistant. The advantage of the braided lines is that they are torsion neutral under rotation. Laid lines used for mooring pendants tend to hockle under rotation and load.
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