Reason for Underlayment

• The underlayment is installed as a cushion and sound barrier between the sub-floor and laminate flooring. Laminate flooring is installed using a "free-float" method where the flooring is not mounted to the sub-floor. The flooring is actually on top of the sub-floor without the use of nails or fasteners. The underlayment serves as an insulating cushion for the laminate flooring.
  
  

Other Purposes

• Another purpose for the underlayment is to absorb any minor flaws or small bumps in the sub-floor. Underlayment will not even out major holes or deep ridges in the sub-floor. Those types of problems should be repaired before placing your underlayment on the floor. Underlayment also softens the feel of the laminate floor when you are walking on it, but it is not like carpet padding. You will notice only a slight cushion.
  
  

Underlayment Types

• There are four types of underlayment---standard foam, combination foam/film, modified (upgraded) and solid cork. Standard form has a 1/8 inch thickness, inexpensive and is ideal for sub-flooring that has no contact with any moisture or the ground. Standard underlayment doesn't contain a moisture barrier.
  
  Combination foam/film underlayment offers a moisture barrier and the same thickness, sound reduction and sub-floor problem correction as standard underlayment. Combination foam/film underlayment is about the same in price as standard underlayment.
  
  Modified (upgraded) underlayment comes in different thickness levels and is usually manufactured out of a higher density foam or rubber. It also reduces more sound than standard or combination underlayment. The sub-floor correction is the same as with the other two underlayments. Modified (upgraded) underlayment is slightly higher in price than the other two.
  
  Solid cork underlayment offers the maximum in sound reduction and used mostly in apartment and condominium construction. It is much higher than the other three in price because it is manufactured out of cork. The cushion level is the same as the other three. Note, the sub-floor must be totally flat before installing this type of underlayment.