Rackets are a sandwich. The outer layers are made of some fiber with resin, the interior is made of some foam material.

 

Outer layers are mostly either fiberglass or carbon, of course there are variety of carbons and there are also mixed fibers with carbon and fiberglass or kevlar and other materials. This is a whole word but to break it down, full fiberglass rackets are cheaper and softer, and have less durability also. As the pretensions for the racket increase you might see mixed carbon and fiberglass to have intermediate characteristics and for top end rackets you have full carbon rackets. Carbon comes in varieties and the rule of thumb is that the less K the carbon is described with, the harder it is, e.g. 3k carbon is harder than 12k carbon.

 

The interior foam can have different properties but basically they can be more or less reactive or hard. In the Argentinian market you'll find some rackets that are marketed as having EVA or FOAM in the interior, EVA-marketed rackets are usually harder than foam ones. In the rest of the markets you won't see that distinction, but there is variety on that material, high-recovery, black eva, 30 vs 50 hardness in starvie, there is variety there.

 

The combination of interior and external materials will determine the hardness and feel of the racket, where you have soft and cheap rackets for beginners, with the cheaper ones made in fiberglass completely or partially and price and hardness tipically increase for more advanced players, with rackets that are fully composed of carbon fiber above the 150EUR mark or so. There are soft rackets that are full carbon and expensive but this is not really true of the opposite.