 Smoke is differentiated from other atmospheric effects in that it is composed of solid particles released during combustion, rather than the liquid droplets that fog or haze are composed of.Fog is created by pumping one of a variety of different glycol or glycol/water mixtures (referred to as fog fluid) into a heat exchanger (essentially a block of metal with a resistance heating element in it) and heating until the fluid vapourises, creating a thick translucent or opaque cloud.Devices specifically manufactured for this purpose are referred to as fog machines.