Can I use the same underlayment for vinyl and laminate?

Sometimes, but check the label. Laminate and engineered wood use thicker 2 to 3 mm felt or foam underlayments. Thin click LVP needs a firmer, thinner pad rated specifically for vinyl, because a soft, thick pad can flex the planks and break the joints. Many brands sell an LVP-specific version.

Is thicker underlayment always quieter?

Not necessarily, and it can cause problems. Sound performance comes from the material and its IIC/STC ratings, not just thickness. Going thicker than the flooring maker allows makes a floating floor spongy and stresses the locking joints, so match thickness to the spec rather than maxing it out.

Do I need a vapor barrier on a wood subfloor?

Usually no. Vapor barriers are for concrete and other below-grade or ground-contact slabs. Over a plywood or OSB subfloor above a dry, ventilated space, a vapor barrier can trap moisture between layers, so most manufacturers advise against it there. Follow the specific product instructions.

How to Choose Flooring Underlayment

By The DIYPicks Team · Updated July 2026

Underlayment is the thin layer between your subfloor and a floating floor. Chosen well, it makes the floor quieter, warmer, and safer from slab moisture. Chosen poorly, or doubled up, it can make a floor spongy, stress the click joints, and void the warranty. This guide explains the few decisions that actually matter so you buy the right underlayment, or correctly decide you do not need a separate one at all.

Attached Pad vs Separate Underlayment

Many laminate and most rigid-core vinyl planks come with a pad already bonded to the back. If yours does, you should not add a separate underlayment on top of it. Stacking two pads makes the floor too soft, lets the planks flex, and can crack the locking joints over time. It also commonly voids the flooring warranty.

If your planks have a bare backing with no attached pad, then a separate underlayment is where you get sound control, cushioning, and moisture protection. Check the back of a plank or the spec sheet before you buy anything.

Moisture Barrier Over Concrete

Concrete slabs, whether on grade or below grade, constantly release moisture vapor. Without a barrier, that vapor can damage flooring, promote mold, and void warranties. Over any concrete subfloor you need either an underlayment with a built-in moisture or vapor barrier or a separate 6-mil polyethylene sheet.

Products like QuietWalk Plus and FloorMuffler UltraSeal have the barrier integrated, so you get sound control and moisture protection in one roll. Over a wood subfloor above a dry, ventilated crawlspace or a heated basement, a vapor barrier is usually unnecessary and can even trap moisture, so match the barrier to the situation.

Sound Ratings: IIC and STC

Two numbers describe how well an underlayment blocks noise. IIC (Impact Insulation Class) measures impact sounds such as footsteps, and STC (Sound Transmission Class) measures airborne sound like voices. Higher is better for both.

For an upstairs room over a living space, look for IIC in the high 60s or 70s. QuietWalk Plus (IIC 71) and FloorMuffler UltraSeal (IIC 74) are both strong performers. If you are on a ground-floor slab with nothing below, sound rating matters much less and you can prioritize moisture protection and cost.

Thickness and Subfloor Smoothing

Underlayment is not a leveling product. A typical 1.5 mm to 3 mm pad smooths only very minor imperfections; it will not fix a dipped or humped subfloor, and installing over an unflat surface leads to hollow spots and failed joints. Flatten the subfloor first with patch or leveler.

Thicker is not always better. Too much cushion under a click floor causes the same joint stress as a doubled pad. Follow the flooring maker's maximum underlayment thickness, which for many rigid-core vinyls is 1 mm to 1.5 mm and for laminate is often up to 3 mm.

When NOT to Add Underlayment

Skip separate underlayment when your planks already have an attached pad, when the manufacturer's instructions forbid it, or when you are gluing the floor down (glue-down installs bond directly to the subfloor). Adding a pad in these cases does more harm than good.

The one exception with an attached-pad floor is moisture: over concrete you may still be required to roll out a thin poly vapor barrier under the planks, but nothing thicker. When in doubt, the flooring manufacturer's spec sheet is the final word, because it is what the warranty is written against.

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Frequently Asked Questions

Can I use the same underlayment for vinyl and laminate?: Sometimes, but check the label. Laminate and engineered wood use thicker 2 to 3 mm felt or foam underlayments. Thin click LVP needs a firmer, thinner pad rated specifically for vinyl, because a soft, thick pad can flex the planks and break the joints. Many brands sell an LVP-specific version.
Is thicker underlayment always quieter?: Not necessarily, and it can cause problems. Sound performance comes from the material and its IIC/STC ratings, not just thickness. Going thicker than the flooring maker allows makes a floating floor spongy and stresses the locking joints, so match thickness to the spec rather than maxing it out.
Do I need a vapor barrier on a wood subfloor?: Usually no. Vapor barriers are for concrete and other below-grade or ground-contact slabs. Over a plywood or OSB subfloor above a dry, ventilated space, a vapor barrier can trap moisture between layers, so most manufacturers advise against it there. Follow the specific product instructions.