Which to Buy
Underlayment comes in long, narrow rolls of about 100 square feet (for example, 44" wide by 27.3' feet long) and around 3 mm thick.
Light Foam: About half the cost of felt, polyethylene foam is the cheapest underlayment you can buy.
At 1.5 pounds per 100 square feet, this 3 mm thick foam underlayment smooths the subfloor but does little to absorb sound.
Heavy Foam: Heavier, more expensive closed-cell foam underlayment. At 2.2 pounds per 100 square feet, this material has better sound absorption qualities vs. the lighter foam but does not approach felt's heaviness.
Felt: Recycled fibers compose felt underlayment. This 3 mm thick underlayment has a heavier, more cloth-like feel and tends to smooth down better than foam underlayment. Weighing 12.5 pounds per 100 square feet, felt underlayment is over 450% heavier than foam. Denser, heavier materials tend to absorb sound better.
Purpose of Underlayment
As a result, you need to provide extra cushioning and sound absorption properties to your laminate.
Without underlayment, your new floor will be harder on your feet. Noises will more easily transmit to floors below, as well as within the room where the laminate is located.
But the main purpose of underlayment is to provide a smooth, flat surface, reducing subfloor imperfections that may "telegraph" to the flooring surface.
- Provides your floor a bit more thermal insulation.
- Bridges minor gaps that subfloors or existing floors have.
- Absorbs some sound.
- Makes it easier to walk on.
- Acts as a moisture barrier.
Floors That Come With Pre-Attached Underlayment:
With these types of floors, it is not only unnecessary to add underlayment--the quality of your installation will be detrimentally affected. You will end up with a floor that is too squishy and does not wear well.
Do You Really Need It?
In some cases, underlayment will not make an appreciable difference in your end result.
If laying laminate on a smooth wood subfloor, the inclusion of underlayment will not make the floor warmer or quieter. If anything, underlayment may give the laminate a mushy, swishy "laminate floor" feeling. It's a feeling that real solid wood flooring does not have.
At $0.25/square foot, underlayment is not particularly expensive. But if you're trying to go cheap by installing that $1.00/sq. ft. laminate, underlayment increases the total price by 25%.
Not Meant As Primary Moisture Barrier
Be sure to check product specifications.
If you are laying laminate over concrete, for example, you need a vapor or moisture barrier. Check product specifications to see if the underlayment will act as a vapor barrier.
Not For Warmth: For That, Try Radiant Heating
Even though underlayment can help make laminate feel warmer, it will not do much to help excessively cold floors, such as basements located in chilly climates.
- Sizing: Make sure that the underlayment is as least as long as your room. This helps you avoid unnecessary seams. For example, if your floor is 25' x 25', purchase underlayment in 30 foot long rolls or longer.
- Seams: Length-wise seams are unavoidable. These seams are held in place either by self-adhesive on the underlayment itself or separately with tape.
Note on Terminology
Within flooring, there are two materials that go by the same name of "underlayment." The focus of this article is the soft kind described above. Another material, not covered here, is thin plywood or fiberboard, usually about 1/4" inch thick.