49 CFR §179.202-7
Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
The entire thermal protection system must be covered with a metal jacket of a thickness not less than 11 gauge A1011 steel or equivalent; and flashed around all openings so as to be weather tight. A protective coating must be applied to the exterior surface of a carbon steel tank and the inside surface of a carbon steel jacket.