For paintballing, molded or laminated armor really isn't the answer. Cardboard & ductape will stop a paintball, it's the running, jumping, & rolling around that'll completely trash it, & any of the other common methods.
The #1 material & method for durable 'sporting' armor, is vacformed Kydex. It's the plastic used for Sampsonite luggage, & a great majority of the hockey, biking, and other impact sports equiptment out there...
For the most part, it works just like styrene or ABS when it comes to cutting & vacforming, except it takes a higher heat and more vacum pressure to pull it over the bucks. Once it's cooled, you can beat it with a hammer all day long.
So... When it comes to vacforming, styrene for looks, cheapest. ABS for decent strength & durability, aboiut twice as much as styrene cost-wise. Kydex for the adreniline crazed... You might get mangled, but your armor will still look great... About 2 to 3 times as expensive as ABS...
I use 1mm styrene for most of my prop & costume forming. Most of the more durable 'trooper' type armor uses 2mm, which gives a fairly durable piece. A 4' x 8' sheet of 1mm to 2mm styrene should run you about $20 to $35 a sheet, depending on your supplier. I recommend finding one as close as possible, as shipping can cost more than the plastic. Look in the yellow pages under plastic suppliers / manufacturers... Most suppliers can provide styrene in a few different colors besides white... I usualy get all mine in black, but I've seen green, tan, gray, red, etc...
If you are careful, you can get an entire suit out of one sheet. I recommend a 2' x 2' forming table & frame, & if you have the ability, a matching heater. I've built several of both, usualy costing less than $30 for both heater & vac table...
My first one was built for free out of an old space-heater, a broken vacum cleaner, & some scrap wood. I use 3 different rigs right now, my original 'scrapper' which is sized for plastruct/evergreen sheets (12"x7") & can be adapted for 12"x12", my medium which is 12"x18", & my large which is 18"x24"... I built the last 2 specificly sized for a batch of styrene I got that was precut to 18x24... I've got materials set aside for doing a 24X24 next month for larger projects...
I have 2 excellent 'how-to' books on vacforming, from making your own heater, to everything else... It's suprisingly easy... It's also suprising how fast you can go through alot of styrene when having fun...
I'll run them through my scanner & get them online...
Wolf