Inflamable vs. combustible
The Spanish words inflamable and combustible both refer to things that can burn, but they indicate different levels of fire risk and possess different grammatical uses. The word inflamable specifically means highly flammable and describes materials that ignite very easily at normal temperatures. Meanwhile, combustible describes materials that can burn but usually require higher temperatures to ignite, and it is also broadly used as a noun meaning fuel.
Inflamable
The adjective inflamable describes a highly volatile substance that easily catches fire and burns rapidly under normal working temperatures.
El alcohol puro es un líquido muy inflamable que debe manejarse con cuidado.
(Pure alcohol is a highly flammable liquid that must be handled with care.)
Los bomberos descubrieron varios tanques con gas inflamable dentro del edificio.
(The firefighters discovered several tanks with flammable gas inside the building.)
Las latas de pintura en aerosol suelen llevar una etiqueta que indica que su contenido es inflamable.
(Aerosol paint cans usually carry a label indicating that their contents are flammable.)
Está prohibido fumar en esta área debido a la presencia de material inflamable.
(Smoking is prohibited in this area due to the presence of flammable material.)
Esa tela sintética es altamente inflamable y no se recomienda para la ropa de cama.
(That synthetic fabric is highly flammable and is not recommended for bedding.)
Combustible
The word combustible can be used as an adjective for materials capable of burning when sufficient heat is applied, and it is heavily used as a noun to mean fuel for machines and vehicles.
La madera seca es un elemento combustible excelente para iniciar una fogata en el bosque.
(Dry wood is an excellent combustible element for starting a campfire in the forest.)
El avión tuvo que aterrizar de emergencia porque se estaba quedando sin combustible.
(The airplane had to make an emergency landing because it was running out of fuel.)
El papel y el cartón son materiales de tipo combustible que abundan en las casas.
(Paper and cardboard are materials of a combustible type that are abundant in homes.)
Muchas personas buscan un coche que consuma menos combustible para ahorrar dinero.
(Many people look for a car that consumes less fuel to save money.)
El carbón es un mineral combustible que se ha utilizado durante siglos para generar energía.
(Coal is a combustible mineral that has been used for centuries to generate power.)
Summary
In summary, use inflamable to describe things like gasoline, alcohol, or hairspray that catch fire very quickly and easily. Use combustible as an adjective for things that can burn but require more heat to start, like wood or paper, or use it as a noun when you want to refer to everyday fuel.