Flammable and inflammable both describe something that burns easily and quickly, but most people use flammable because inflammable looks as if it means not flammable.
( inflammable, especially in BrE) VERBS | ADVERBVERBS➤be易燃ADVERB➤extremely, highly, very (NAmE) 極其/高度/非常易燃◇These materials are highly flammable.這些材料極其易燃。