When Byrne was re-envisioning the character, he had the perfect explanation.
The costume wasn't Kryptonian .. it was made of very earthly materials. It was the fact that Clark had a very thin aura around him that made him and anything within a few milimeters of his skin invulnerable. Like a very tight force-field. Therefore, having his costume very tight helped protect it. It's why Bryne had all those great shots of Supes in battle with his cape torn but the body of the costume intact.
Byrne was and probably still is a great idea man. His writing may not be up to Alan Moore level but his ideas are solidly thought out.