> That's a pretty sharp cuttoff. OTOH, from this scale you can't tell
> whether the filter still passes, say, 1% of the UV. 1% UV is presumably
> still easily enough to utterly destroy whatever is underneith. (E.g., a
> plastic coated in this stuff will get ruined in a few months rather than
> a few days.)

I don't think many dyes fade within a few days of sunlight exposure. A 
few months maybe, but then a 1% UV filter will allow them to last a few 
decades, which is actually useful for something like a car or a photo.

> So... essentially you're saying the only real change is that plastic is
> cheaper now?

Not really, what I'm saying is that the development of plastics and the 
processes that use them have allowed *products* to become cheaper. But 
that's pretty much the entire purpose of engineering, to make a product 
that meets all the requirements for as low a cost as possible. If you 
can come up with a new material (or a variant on an existing one) that 
allows an existing product to be made cheaper you will be collecting the 
$$$.

> I knew there were at least 6 main plastic types.

Correct, there are at least 6 :-) Here's a list of the common categories:

http://www.efunda.com/materials/polymers/history/history.cfm?list_order=name

There are about 40 there. If you click on each one it will give you a 
list of common grades, about 20 for each of the ones I clicked on. 
That's already 800 different grades without even considering various 
combinations of other additives to aid manufacturing or specific 
properties needed. My point is that if you plot all of these on a 
timeline you'll see that most have been developed fairly recently, it's 
not like there's no development in plastics.

> (Also, if this plastic as such a high melting point, how do you mould it
> in the first place??)

Make your manufacturing machinery from something with a higher melting 
point, say steel? How do they make the steel in the first place? :-)

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