Purposes

• The purpose of underlayment for laminate flooring is to cover up minor defects in the subflooring so the laminate will lie flat, reduce noise and act as a cushioning when you walk on the floor. Some laminate flooring underlayments also provide some heat insulation, act as a moisture barrier or have an antimicrobial agent embedded in them. The R-value of most underlayments is low, so you should not make this a major criterion. The efficacy of antimicrobial agents in underlayments also is questionable. Choose your underlayment for its sound reduction and cushioning value.
  
  

Cautions

• Before you do anything else, you should choose what laminate flooring you will be using and read the installation instructions and warranty. Some manufacturers suggest specific underlayments, which should work better with your flooring than other choices. Further, not using underlayment, or the kind of underlayment the manufacturer suggests, could void your warranty. Carpet padding is not the right underlayment for laminate flooring.
  
  

Installation Restrictions

• Which underlayment you choose will depend in part on where you are going to install your laminate flooring. If you are laying it on a concrete subfloor, the underlayment must include a moisture barrier, or you must lay polyethelene film under the cushioning underlayment. Above grade plywood subfloors should not have a moisture barrier because blocking vapor can cause mold problems. Do not use an underlayment with a moisture barrier unless you need it.
  
  

Underlayment Materials

• Underlayments for laminate floors can be made of rubber or cork, but most often you would choose a foam underlayment. A standard foam underlayment is about 1/8-inch thick and does not have a moisture barrier. A combination foam/film underlayment is the same as the standard foam underlayment but has a moisture barrier on the bottom. This underlayment should be used if there is even the slightest possibility of moisture coming up from the subfloor. Replacing moisture-damaged laminate flooring would be a lot more expensive than using a moisture barrier in the first place. Upgraded foam underlayments come in different foam thicknesses and densities, or they can be made of rubber or fiber. They offer somewhat more sound protection than do the underlayments above. You could use a solid cork underlayment, but usually the expense would not be justified unless you need maximum sound reduction. Solid cork underlayment is sometimes required in condo buildings.