If the floor is cement, make sure the cracks are filled. Tackless Strip - A tackless script is a wooden batten with pins projecting up at an angle. You will want to apply these strips to the ground around the perimeter of the room. This is how your carpet will be held down. Sponge rubber padding and urethane foam padding will not mildew.
Urethane is just thicker than the sponge.
Whichever you choose, attach it to the floor with a staple gun. Make sure it reaches the tackless strip. Trim Carpet - Before you purchase your carpet, you will want to measure the room. Try to get the largest piece available, so you do not have to join many sections of your carpet. If you need to trim it, mark the back side with a chalk line, then cut it with a utility knife.