I. J. Thompson said:
The difference between resin and metal is obvious, but the difference between resin and plastic isn't so much, to a layman such as myself. Can you describe, or point us to some info?
Resin is... well, resin, and plastic comes in three forms, so far as hobbies go: polyethylene, which is the squishy soft plastic that is incredibly durable but does NOT take paint well and goes all bendy; polystyrene, which is the hard plastic that model kits have been tradionally made from; and ABS, a newer hard plastic that has improved properties.
Polyethylene & resin need to be glued with superglue or epoxy. These glues do not affect the material, but just bond them together as best as can be. Both these mediums need to be washed with a mild detergent, or rubbing alcohol, prior to any attempts at gluing or painting as they carry mold residue that will repel both glue & paint.
Polystyrene & ABS are much easier to work with, and are assembled with model glue. This glue actually sorta melts or disintegrates the plastic itself, allowing the two parts to actually merge a bit, and when dry forms a solid bond. This also means, "less is more" with model glue. The biggest mistake novice modellers make is going buck-wild with the cement. For assembly, washing is not necessary but if you have big, smooth surfaces I'd still wash 'em first to allow the (later applied) paint to adhere better.
A final note: Resin can actually be used by amateurs in the home. Plastic... eeeh, not so much. SO, you can get this awesome variety of what are called "garage kits" made at home by very talented folks who produce kits of unusual subjects the Big Dogs won't touch. These are obviously labor-intensive and the molds don't last too long and, combined with the cost of materials & small production runs, are far more expensive than equivalent styrene kits from Revell, Pegasus or whatever. Nonetheless, some of 'em are reeeeally worth it. I recently surrendered seventy bucks for an 11" long kit of the Star Wars Dreadnought (THAT'S a big hunka resin!), and just (after three years of trying) finally won a 12" model of the Discovery from 2001 for the base price of $40 (free shipping). Boo-yah!!