New TTI Headers - What Gasket?

Question for those who have used Remflex. What are they constructed of?
Also anyone use soft copper, if so what brand?
Remflex exhaust gaskets are made from 100% flexible graphite and can withstand up to 3,000 degrees F—so they are not affected by exhaust system, and won’t burn out, shrink, or leak. From the Remflex Site.