[Update] I have written a lot about Dyneema standing rigging so I now have a guide to it all in: Dyneema / Synthetic Rigging Summary[End Update]
Until recently the answer would be: terrible. A “plastic” made with petrochemicals that can’t be recycled.
However, things are changing.
There is now a Bio-based Dyneema fibre which has International Sustainability and Carbon Certification (ISCC).
What isn’t quite so clear is which companies are using this and in which products. Marlow ropes announced that they were using Bio-based dyneema in July 2020. Liros also have an announcement but I can’t find product detail. Given it is so new it might take a while to work through the supply chain.
There are also initiatives to accept “retired” ropes back for recycling, it looks like we can be fairly confident that any ropes we buy now for standing and running rigging as well as dock lines etc will all be recyclable (and some companies like Marlow are already making some ropes from recycled plastic).
I confess I’m pleasantly surprised by what I have found. Looks like this is much better than I expected. The only issue will be the microfibres of plastic that get shred into the water during the lifetime of the ropes. Not sure what can be done about that, but at least compared to other forms of plastic pollution this is a significant improvement.
[Update] thanks to twitter there is another option for Bio-based Dyneema: Gleistein
Gleistein is adopting the world’s leading role among textile rope manufacturers – being the first to switch its entire production of products made with Dyneema® to bio-based fibres. Read our factsheet: https://bit.ly/2UKFrKA