Smooth Surface

• Laminate flooring is thinner than solid wood flooring and more readily shows imperfections or bumps in the subfloor. An underlayment can smooth out the surface of the subfloor, hiding minor imperfections and improving the laminate floor's appearance. Underlayment products vary in their ability to hide imperfections, based on the material and the thickness of the underlayment. If the floor is severely damaged, replace it or cover it with a plywood subfloor prior to installing the underlayment.
  
  

Sound Reduction

• Laminate floors, unlike most solid hardwood floors, are not glued or nailed to the subfloor. Instead, these floors are glued or locked together, and float on top of the subfloor. Because of this installation method, laminate floors can be noisy when you walk across them -- a problem that is especially noticeable under upper floor rooms. Underlayments can act as a sound barrier, absorbing the noise to make a quieter floor.
  
  

Comfort

• Depending on the underlayment material and its thickness, an underlayment can provide a cushion for the laminate floor, making it more comfortable to walk on. This is especially important if the floor is installed over a cement subfloor.
  
  

Moisture Barrier

• In areas, such as a basement or laundry room where moisture might seep up through the cement, a plastic or vinyl underlayment protects the floor from warping due to moisture. This plastic liner may be attached to the underlayment, but, in most cases, you'll need to lay an additional layer of plastic next to the cement, beneath the underlayment.