Most kitchen cabinets are made of a variety of materials depending on how much they cost.  Most will consist of particle board, plywood, solid wood and medium density fiberboard (MDF).  Particle board tends to be the main ingredient to kitchen cabinets with the lower price tag.  Particle board is made up of wood shavings, sawdust and other wood products that are pressure glued together. Plywood is made up of layers of wood plies on top of each other which provide good strength in all directions because it is the same material layered on top of each other.  Medium density fiberboard is a material made of finer components then particle board but unlike particle board can be molded and shaped because it is smoother and its surface can be painted or stained. 

When looking for good quality cabinets try to stick to plywood.  Many people get the misconception that solid wood is the best quality cabinet—when in fact that is not true.  Solid wood cabinets tend to absorb moisture, becomes unstable and can then shrink and swell depending on the humidity. Make sure that when you are doing your research you ask what the cabinet is made of, if they tell you solid wood they are usually referring to plywood with wood veneers so make sure to verify.  Solid plywood is ideally what you want to be looking for without and particle board, MDF, or veneers. Veneers can be used over solid wood door and drawer fronts which are usually for aesthetic purposes and will not affect the actual durability or quality of the cabinet. The cabinet sides, back, top, bottom, drawer boxes and shelves are the main ingredients of a kitchen cabinet. In a quality made kitchen cabinet, those components would ideally be constructed of plywood.

The most important thing about renovating, remodeling or installing new kitchen cabinets is to be as well informed as you can.  Do the research before you shop so you can be an informed customer who purchases a good quality product.