You need to go to the West Coast Art & Framing Show at the Mirage Hotel in Las Vegas. Every major framing supplier will be there, including the moulding manufacturers and distributors. Universal, Omega, MyMoulding, TenPlus, Chelsea, Delta, and many other moulding distributors will be showing lots of poly moulding, in addition to their normal lines. Every year we see more poly being featured.
http://www.wcafshow.comThe trade show runs Jan 30 to Feb 1. You can also sign up for classes in basic and advanced framing topics, but it's getting late.
But please do not order any moulding based on website images or pictures in catalogs. You can be unhappily surprised. Always call up and ask for a "chip" which a 6 inch section, or for a corner sample. If I'm in a hurry and a new moulding looks hot, I will sometimes order "three sticks cut in half" which gives me enough to make 2, 4 foot wide panoramic ratio frames for evaluation and customer comments. And I make a point of asking for "current stock" because every time a new batch of any type of moulding is run, there are often big changes, and I just got bit hard by that a few months ago. So the wise thing is never order box quantities (boxes contain 70 to 180 feet) until you see a current sample, and your first box orders of a new style should only be for 2 or 3 boxes until you see how well the boxes are packed and how well your customers like it, and how easy it is to work with.
I could go on, and on. You will find stuff online that merrily tells you that poly can be cut and joined just like regular wood moulding. That is total BS! Poly is a whole different beast than wood and you need to treat it as such or your frames will fall apart in very short order, although a properly made poly frame is as strong as wood and much longer lasting.
Which leads me suggest that you check out the major US framing forum for more info on joining poly. Some of it even makes sense. Just remember framers are often quite resistant to poly for many reasons not necessarily relating to the material itself. Let your happy customers be the ones to pass judgement.
http://thegumble.comAnd to your question, poly has a bubbly, finely-foamed interior that is much harder and denser than styrofoam. It varies a lot. Usually there is a plastic veneer applied over that which gives the moulding its appearance. A few of the veneers look subtle and elegant, but most look like shiny plastic. Be discerning and make careful choices, that's the key.