of all the fibers. When Dyneema is covered with polyester it's to protect the core from UV and to give it better "hand", and allow it to be gripped by rope clutches (Dyneema is naturally slippery). But the polyester is actually less resistant to UV than the Dyneema.

They say the sock in these clutches is coated for better UV resistance, and grip. It's replaceable, but I assume it's good for 7-10 years depending on exposure.