I've always been meaning to post this, but it kept slipping my mind. It's a pretty good analysis of Superman's difficulties in reproducing.
http://www.rawbw.com/~svw/superman.html
http://www.rawbw.com/~svw/superman.html






According to Superman #146, Martha Kent was moved to fashion a super-playsuit for the infant Superman because the child was constantly destroying his store-bought clothes by engaging in various forms of super-powered play. Fortunately, the Kents had had the foresight to save the three blankets - one red, one blue, and one yellow - in which the infant Superman had been swathed when he arrived on Earth in his rocket. Because the blanket material was indestructible and therefore could not be cut by any scissors, the Kents unraveled some loose ends and then coaxed their super-powered infant into using the heat of his X-ray vision to cut the unraveled thread so that Martha Kent could use it to sew the Kryptonian blankets into a super-playsuit. Years later, Martha Kent unraveled the playsuit and rewove the thread into Superman's now-famous costume. According to one of the stories in Superman Annual #8 (1963), the young Superman used "strips of rubber padding" salvaged from the wreckage of his rocket to fashion a pair of bright red boots, while a yellow strap, also salvaged from the rocket, became his belt.