The most common and most likely answer to this crossword clue is the 8 letter word ASBESTOS
I've seen this crossword clue in The Guardian
A
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More clues leading to the result ASBESTOS
- A plea for help to tackle leading cause of cancer
- Most advisable to enter a call for help for material needing removal
- Hazardous material? Put a distress call around first
- Dangerous material? Most suitable to engage in a plea for help
- When cream turned thus, one mustn’t sniff it
- Potentially dangerous mineral like prime salt
- Arsenic of highest quality, huge danger to health
- I might end up lagging, like worst cartographers
- A cry for help brings in top firefighter
- Fibres for protective coat and top stocked by fashion e-tailer
Buddy explains!

The straight part
We know that "heat-resistant material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case heat-resistant material = asbestos.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ASBESTOS mean?
ASBESTOS noun- Any of several fibrous mineral forms of magnesium silicate, used for fireproofing, electrical insulation, building materials, brake linings, chemical filters, suits, fireman's gloves, etc.
- Any of asbestos-like forms of several minerals, asbestiforms