Comparison shop? Oh, Hell no! Find someone you trust, a professional who has very high standards and lots of experience, and pay them the premium that quality commands. If it's about saving money, you are in the wrong hobby. And what is this online nonsense? I treat framing choices as art, and spend quite a bit of time touching, feeling, looking, pondering. 

Normally if they use conservation materials they add a sticker to the rear of the frame and tick products used.

My local framer said he can tell by looking if UV glass has been used, so I guess that's the same for plexi.
Take them to a decent framer to get looked at.

Put on a pair of polarised sunglasses and look at your frame in a well lit Place.

If you see coloured "swirl" on the glass like gasoline in a puddle, you are looking at UV treated glass in 99.9% of cases

If they are expensive pieces or worth protecting, why take a guess and risk having the pieces permanently damaged. UV plexi isn't as expensive as you think and it's inexpensive compared to the damage that can be caused over time by damaging rays. Even if you can detect it does have some UV protection, you will not know how much protection unless it is marked. They usually range from around 66% to 99% protection. You'd be surprised how many framers use the 66% by default and many customers don't even know to ask what % they are getting.  Also if you have not already, it is important to open the frame and inspect the mounting and materials used anyway which can be done in the replacement process. 

If you have a good relationship with your framer possibly as him what brand plexi he uses and see what the protection is from that make and line. As mentioned it it is a valuable piece to you why risk it, just have it replaced with the plexi you choose. I have been using museum plexi for my top pieces which is fantastic at eliminating reflections as well as UV protection but it is more than double the price of regular 99%UV plexi.  

I always go museum plexi (instead of museum glass, which can shatter; we get plenty of earthquakes here) for my most prized prints that I want to enjoy for as long as possible. I have a low tolerance for reflection as well, so museum works well. For everything else, there's UV plexi.

Probably one of the few.

I don't go all out for museum but always with UV glass or UV plexi.

Sorry to necro this thread but I'm currently weighing up whether to use museum plexi or museum glass on a new purchase. It's a print with a dark background and is being shipped in the frame from the Netherlands to the UK. When it gets here it will pretty much be the pride of my collection so I'd rather spend a bit more to get the best result, both in terms of aesthetics and to protect it in the long term. I've seen different opinions on the thread so far - plexi can scratch easily but glass can shatter. Any more opinions? And what are your views on how easy it is to keep them both clean?

Thanks. Much appreciated.

Street lighting is going all modern now with LEDs

 I guess it depends on what one can live with. If it was me I would use ordinary glass or anti uv glass and spend the money saved on a really good frame and mount job.

I'm not sure who your post is aimed as I haven't seen anyone banging on about museum glass or anyone say it's just a 'little bit more'.

Two things - Firstly, there's people on here with different budgets and different priorities. I've seen posts where people have been willing to bid thousands at auction or drop upwards of £10k on a piece. That's totally beyond me. Elsewhere on this thread people have said they'd rather buy fewer pieces and make sure they pay more on framing. Just different people choosing how to spend their own money.

Secondly, it does seem we're getting a pretty crap deal in the UK. I'm literally spending about twice as much as it would cost to get regular UV glass to get museum for the piece I'm getting from the Netherlands. I think someone from the US said the price difference was less there as well further up the thread. Wonder why it's so much here.

That's a relief. I thought I'd somehow managed to offend a forum mainstay in my first week of posting.

For a valuable or expensive print. I agree it's worth protecting the item so it stays in pristine condition. Acrylic is less expensive and does the job ok. For less expensive art is it worth the cost ? These days most prints are printed with lightfast inks and the paper is acid free and are usually hung away from any direct sunlight or walls facing windows for best protection.

Here is the True Vue site with their find a local distributer in different countries page. tru-vue.com/find-a-distributor/

Here is a supplier that ships the glass with prices. www.c4gallery.com/merch/tru-vue-museum-glass.html

Here is a camera forum discussing the glass and it's price.

forum.luminous-landscape.com/index.php?topic=51201.20