Flash has an aura around his body that protects him from the side effects of moving at great speeds.
Superman's suit, in some incarnations, is from Krypton and is just as invulnerable as he is. In others, Superman's body projects an energy field that contributes to his seeming invulnerability which makes his suit virtually indestructible. His cape, which is out side of the field, tended to get shredded. Currently Superman is pretty tough but uses his cape and Kryptonian armor to make himself invulnerable.