Originally Posted by tw2

Cracking is a result of material being too think. Poor quality material with imperfections and impurities in the metal. Inadequate weld penetration. Uneven weld penetration. Not back purging will allow for hot spots to form. Basically cracking is due to poor manufacturing or excessive stress, ie inadequate support.

The heat used in welding is far in excess that of exhaust temperatures. Any heat wrap helps to keep exhaust temperature high which is your aim. If you want your headers to be cool your thinking is incorrect. Heat cycling destroys poorly made products not heat wrap or ceramic coating.