Let me add another data point to the discussion: my Swaro 8.5x42 SV, bought in 2011.
As can be seen from the metal parts, it has had a lot of use. But no problems whatsoever with plastic armour! I never use DEET and almost never use sunscreen (I use sun gloves instead to protect my hands), so not much chemical exposure. But my bins have had TONS of UV exposure!
I have backpacked/hiked a lot with these bins around my neck, often in areas with very high UV exposure. For example the full Arizona trail (2 months, much of it desert), The full Pacific Crest Trail (5 months, fierce sun almost every day and often high elevation), a total of 8 weeks in Nepal mostly at very high elevation, 3 months hiking in Australia / Tasmania (depleted ozone layer). 2 Months Ecuador (very high elevations), 2 months Ethiopia (high elevation), etc etc... (Also many other travelling and of course on top of that the regular birding and hiking in England and Scotland).
The point I want to make is that in all these cases, the bins were exposed the
entire day, because I almost never put them away in my backpack. So that is many hours of exposure in areas with sometimes insane UV exposure (like deserts and high mountain ranges).
So my conclusion is that
1) At least the armour of the older Swaro (pre FP?) is very durable.
2) It is not deteriorated much by UV
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