Clay Poker Chips
There are three types of materials most poker chips you can buy are made of. The fanciest kind are known as clay poker chips, though truly they're made of a combo of clay and other materials, and are the standard casino diameter of 39 mm. They have a nice heft, and weigh from 8 to 11.5 grams a piece.
Metal Poker Chips
The second kind of poker chips are made of a metal core surrounded by plastic and weigh either 8 or 11.5 grams. These metal-core composite poker chips are the closest match to what you'll find in most casinos these days, and are a good, durable choice.
Plastic Poker Chips
Finally, you'll find plastic poker chips. While they aren't as substantial as the other two kinds of chips, they are a lot cheaper and in the end, do the job just as well. You can find a kind of plastic chip that's better than the kind you can pick up at toy stores and Kmarts, but I'd recommend starting out with the cheapest ones and saving your money for when you can buy metal-core or clay chips.