Carpet pad is the foundation of your carpet. It can change everything from comfort level to the length of your carpets life. You have an option to choose from 5 different types of pad, Waffle Rubber, Re-bond padding, Foam, Fiber, and Slab rubber. All have good qualities that you want to look for in your selections.
You can change pad types through your house to meet the needs of individual rooms. In heavy traffic areas like your living room you will want a heavy thinner pad, in areas like a bedroom you can switch to a softer thicker pad. Yes, I said thinner in high traffic areas. If you use a thick pad your carpet will flex more and start to wear down faster.
If you are carpeting a basement or tile area you will want to use rubber pad. They are insect proof, mildew proof, and non allergenic.