Originally Posted by Brian Braddock
I dont think an explanation with the suit is even needed. I think the audience would accept a different costume in the same way that they assume Iron Man will have new armor for every movie - just as IM upgrades his armor, Cap is constantly being provided with upgraded costumes/outfits which are improvements on each of their predecessors but may change a bit stylistically.
Note that he has a good excuse: serious combat tends to leave his outfit tattered. Even if they didn't actually change the design, he'd need a new costume pretty often, anyway. He's not Superman with the invulnerable spandex.