[TexasGator]

“Yes, I should have said “Un-Flammable.””

You should not say “Un-Flamable”.

https://www.powerthesaurus.org/unflammable/definitionsadjective
Not capable of catching fire and burning; not flammable
from
incombustible

https://www.powerthesaurus.org/unflammable/definitions

[DiogenesLamp]

You should not say “Un-Flamable”.

If you understand what it means, then the word is fine.