What underlayment goes under laminate?

Before anything else, look at the plank itself. Every laminate line we carry falls into one of two categories on this, and a quick check at the counter tells you which one you're holding.

The first check: flip a sample and look at the back

Flip a sample over at the counter. If there's already a thin foam layer bonded to the back, <a href="/materials/attached-underlayment-laminate/">that's attached underlayment</a>, and the cushioning question is already answered by the box. If the back is bare, hard core with nothing on it, the underlayment is a separate product you choose and roll out yourself before the floor goes down.

What that check tells you, and what it does not

Knowing whether your plank has attached pad tells you whether cushioning and sound deadening are already built in. It does not tell you whether you need a moisture barrier, because that's a subfloor question, not a plank question, and the two get confused constantly. Attached underlayment quiets a floor. It does not automatically block moisture rising from underneath, and a separate vapor film may still be required depending on what's beneath the subfloor.

The second check: what's under the subfloor itself

This is the check that actually decides the underlayment, and it happens at the free in-home measure rather than at the counter, because it means looking at the actual house. Laminate over a concrete slab, on any level of the house, needs a moisture barrier, full stop, because a slab pushes vapor upward even when it looks and feels bone dry. Laminate over a wood subfloor on an upper level generally does not carry that same risk, though a combination foam-and-film product is still a reasonable choice there for the sound control alone.

Sound is the third thing underlayment controls

Cushioning and moisture aren't the only jobs underlayment does. On an upper floor, especially over a room below that people actually use, sound transmission is a real factor, and a denser combination underlayment cuts down on the hollow, drum-like sound a floating floor can make underfoot. That hollow sound has its own page if it's already the problem you're trying to solve. It's a comfort question rather than a structural one, but it's worth raising before the order goes in if the room below is occupied often.

A moisture barrier isn't the same product as a cushioning pad, even when a combination roll claims to do both at once. The barrier's job is an unbroken layer with every seam taped, because a single gap is where vapor gets through. Skipping the tape at the seams to save a step is a common shortcut, and it quietly defeats the whole point of installing the barrier in the first place.

The mistake the checks are meant to prevent

Stacking a second foam pad under a plank that already has attached underlayment is the most common error, and it's a genuine problem rather than a harmless extra layer. Too much cushion under a floating floor lets the locking joints flex more than they were engineered for, and that flex is what opens a seam over time, right in the traffic lane that gets crossed the most. A lifted seam has its own page if that's already happened to you.

What a spec sheet settles that the back of the plank cannot

The back-of-the-plank check tells you about cushioning. It does not tell you the underlayment's perm rating or its thickness, and those numbers live on the product's own spec sheet and on the underlayment roll's packaging, not on a webpage. They're worth reading before you buy rather than after. A subfloor prepped right the first time is also part of how long the floor holds up, which the lifespan page covers separately, and it pairs with what the plank itself is built to resist from above.