Does UV exposure affect line strength?

I definitely have left lines up for a few days before in remote spots (e.g. camping on an island), and occasionally I’ll meet someone who has a lowline or even maybe a highline that has been up for a year or more.  So, a natural question to ask, is what affect might the sun (UV) and to some extent temperature and humidity variation have on line strength?  Of course we need to remember that not all lines are nylon, so this test definitely doesn’t apply to polyester or dyneema or any other webbing, but for nylon it should hold mostly true.  To control for what we wanted to test I eliminated all other variables by using a brand new 30′ piece of the nicest nylon tubular webbing on the market (Sterling TechTape*).  I left the webbing up for close to 15 months, rigged as a primitive (with girth hitches) between two trees on my parents’ acreage outside of Seattle.

So what did we learn?  Well, it looks like a year worth of Seattle’s UV ain’t so bad for nylon webbing.  A 500lb drop in strength now makes this webbing equivalent to “normal” tubular nylon webbing, and in my opinion is a totally reasonable price to pay for this much UV exposure.  We should, of course, note that the webbing was brand new, so slightly worn webbing might be disproportionately degraded by UV; or some other variable might be at work.  Basically, don’t trust your life to this.  I would not leave a highline up for days or even weeks, and definitely not for months (partly because of the wind that many highlines experience, they are often torn to pieces after just a few days) — but I’d feel a lot better about the idea of throwing some big tricks on a friend’s backyard line that’s been up for 3 years straight.

*Incredibly similar to Balance Community’s SlackSpec; for all intents and purposes they are basically the same webbing, and I believe they are even made by the same mill.