Dacron (DuPont's brand of Polyethylene terephthalate or PET) is used for braided lines and backing - and milk jugs... I think Cortland uses polypropylene (PP) for their fly lines and most of the rest use Poly Vinyl Chloride (PVC - thus explaining why you have problems with them - PVC loses plastisizer very easily.) PolyProp would be better than PVC, but PET might be even better. I'd like to try one of those lines.

By the way, PVC and PET both have specific gravities above 1.0. PP has a specific gravity around 0.9, making it the winner in the floating category. OH... and PP has less stretch than PVC and PET, although PET has much lower elongation properties than PVC.

I would like to see a PP outer core with a PET coating...

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