inflammable vs unburnable

inflammable

adj
  • Incapable of burning; not easily set on fire. 

  • Capable of burning; easily set on fire. 

  • Easily excited; set off by the slightest excuse; easily enraged or inflamed. 

noun
  • Any inflammable substance. 

unburnable

adj
  • That is difficult or impossible to burn 

How often have the words inflammable and unburnable occurred in a corpus of books? (source: Google Ngram Viewer )