rdesign@hotmailwhat can i use as a heat barrier / insulator

What can i use as a heat barrier / insulator to protect sensitive electronic equipment from harsh environments reaching 350-400 C for a duration of 60min max?

Polyurethane is apparently an excellent thermal insulator, but it may be ''too'' good if installed improperly.

The water idea is clever. As long as the water is present but free to boil away and the heating isn't extremely fast, its temperature cannot go over 100C. Water is also very difficult to heat. Is it possible to suspend the electronics enclosure in an open metal drum full of water?

110100101106 years ago
double walls with very fast air flow between them triple walls with water between the first 2 (instant limit to 100 C) and air flow between the next 2 walls
deadend_designs (author)  110100101106 years ago
Well the electronics can be suspended in water, but will have to be in a water tight enclosure. Unfortunately the environment does not aid for static placement of the unit, but instead its constantly turning 360 degrees on (X) and (Y) axis. Stated above : water has an instant limit to 100 C. can you tell me what happens after that? Does it act as a thermal barrier?
you have to supply new water so it wont boil away and dry. you can circulate the water thru external cooler to keep it below 100 C from here on you have exactly 100 C or less do deal with. not 300