I just want to clear up a few things on this thread, because I know they get confusing to a lot of people so I'd like to help set things straight.
I've build combat robots as a hobby for many years now and I know about most of these materials.
Plexiglass is the name brand of sheets of Acrylic used to replace glass windows, hence the name. It's no different then how a lot of people call tissues Kleenex a lot of time. Kleenex = brand name, tissues = generic name for the item.
Also acrylic can be bonded chemically with CA (cyanoacrylite) glue, aka most superglues, to create (supposedly) seamless clear bonds.
On a similar note:
Lexan is GE's brand name for polycarbonate. It's a clear impact resistant plastic which is also used for window replacement.
The differences between acrylic and polycarbonate are this. Polycarbonate is a lot stronger. While in the cosplay field that usually won't matter much, it can. Acrylic tends to crack/fracture like glass does. It can leave some sharp edges and potentially break if you drop it depending on how heavy it is. While polycarbonate won't crack or shatter it's typically a lot more expensive. However if you plan to drill through acrylic be very careful as it will chip or break if you do it to fast.
How to tell the difference:
The best way is to read, wherever you're getting it from will probably say. If you're buying it from the window section of Home Depot or Lowe’s I believe typically acrylic is covered in a clear blue film while polycarbonate is in a clear green film.
If you have some clear plastic and you aren't sure what kind it is there's an easy way to distinguish the two. Take a file or some cutting tool and rough up the end a bit. If it's acrylic it should give off a pretty strong odor similar to the places in malls that do fake nails, because yes, those are made of acrylic.
There are two main
types of resins. Epoxy resin and Polyurethane resin. These can both be used by themselves or with fiberglass cloth.
Polyurethane resin is pretty harsh stuff. It gives off strong chemicals and should be used in a place with proper ventilation. It comes in a big metal can similar to paint thinner and has a small tube of catalyst which is used for hardening. The little tubes of MEKP (Methyl Ethyl Ketone Peroxide) can be bought separately. Each brand will give their own ratios of resin to MEKP but it's typically about 8 drops per ounce of resin. The good part about this type of resin is it dries fast and the ratio is more of an art than a science as the catalyst only creates a chemical reaction that causes heat to cure the resin. If you're a little off in your mixture it will still harden it just might do it too fast or take a long time. This stuff will eat away pink insulation foam, so don't use it on it unless you seal it with something first.
Epoxy resin on the other hand is much nicer to work with. It doesn't have much of a smell at all. It won't eat away at foam. The downside is it typically dries a lot slower than polyurethane resin. Also it typically comes in a part A and part B. If you don't mix them evenly it can end up tacky or take a long(er) time to dry.
There are a lot of other plastics you can use for various things. I'd recommend reading around on distributor’s websites to get more information.
Some of them include:
Polystyrene - Most commonly found as extruded polystyrene, aka pink insulation foam. This is pretty good stuff to work with but the vapors given off when melted or even sanded vigorously aren't healthy, so work in a well ventilated place.
Carbon Fiber - Sold in thin sheets, this is a laminate material often used for it's strength and light weight or because the weave looks nice. You can also lay your own in a similar fashion to fiberglass but I imagine it would be hard to get the weave to look nice.
Polyethylene - This might be outside the scope of most builders on here but it's a nice material to work with. It's easily machined, as a nice smooth slippery texture, and can be dyed with fabric dye. It's commonly found as HDPE (High Density PolyEthylene) or UHMW (Ultra-High Molecular Weight polyethylene). I belive this is the material commonly used for cutting boards so that's what the texture is like.
Where to Buy:
Most of these materials can be bought at local hardware stores, such as Lowe's or Home Depot, but there are a lot of online resources as well. One word of caution though is to watch out for shipping costs on really big or really long pieces.
There are a lot of others too but those are the 3 I most often use. If you're lucky enough to have a Tap Plastics store near you I hear they are really helpful there. I unfortunately live on in New Hampshire.
I hope this helps inform some pople. Just remember there's pleanty of knowledge out there but sometimes you have to look.