SLACKTIVITY (Samuel Volery, Tobias Rodenkirch) has conducted a UV-light-exposition test in a permanent midline that was up for 7 months over summer. The tested slacklines were not in the shade but rigged in full exposition to the sun. Five different Slacktivity webbings were tested:

uv-test-slackline-webbing

The main line as well as the backup have been tested. After about 1500 hours in the sun the breaking strength of the mainline has decreased an avarage of about 8kN (=800kg) and the one of the backup has decreased by about 7kN. The complete study can be read in the following pdf document.

Study of breaking strength reduction in highlines caused by UV-light exposure (pdf)