Flammable substances and inflammable substances are basically imply the same meaning. The substances which have very low ignition temperature are called inflammable substances. These substances catch fire very easily. LPG, petrol, and alcohol are some examples of inflammable substances.
Substances that can burn or undergo combustion are called combustible substances. Paper, clothes, wood, LPG are all combustible substances.
Non-combustible substances do not catch fire easily, as their ignition temperatures are pretty high. For example, sand, asbestos etc.
