Pomades.com explains that the difference between pomade and gel is that pomade holds hair in place well, but the hair remains pliant and relatively easy to manipulate. On the other hand, gel provides hold by hardening hair in place. Gel is also easier to wash out than pomade due to the fact that pomade is made from grease and fatty ingredients which do not wash out of hair easily.
There are two main types of pomade: petroleum-based and water-based pomade. Petroleum-based pomades contain grease and fats that give the hair hold while maintaining shine, while water-based pomades are considered to be better for the hair and scalp because they are water soluble. This makes water-based pomades easier to wash out. Pomade also gives hair a slick, shiny appearance, while gel gives the hair a shiny, wet look.
Gel is generally a thinner consistency than pomade, but it can provide a firmer hold depending on the type of gel used. Lightweight gel does not leave the hair as stiff as heavyweight gel. It is recommended that those with hair that is thin or thinning use lightweight gel, while those with hair that is thick, curly, or wavy should use heavyweight gel.