The cheapest mistake in a laminate install is skipping the underlayment, and the most expensive mistake is using the wrong one. If you are wondering what do you put under laminate flooring in your specific room, the answer depends on three things: the subfloor material, the moisture conditions, and how loud you want the floor to sound when someone walks across it. After installing laminate over plywood, slab concrete, and even old vinyl in a dozen homes, here is the underlayment cheat sheet that prevents callbacks.
Why Underlayment Matters
Laminate planks click together at the edges and float over the subfloor — they never attach directly. Without underlayment between the planks and the subfloor, every minor imperfection telegraphs up through the floor. You hear hollow clicking, feel small bumps, and trap moisture against the bottom of the planks where mold and warping start.
A quality underlayment cushions impact, smooths small subfloor variation up to 3/16 inch, blocks moisture from below, and dampens sound. The wrong choice can void your laminate warranty.
Standard Foam Underlayment
Closed-cell polyethylene foam in 2 mm or 3 mm thickness is the budget default. Costs run $0.10 to $0.30 per square foot. It cushions noise and bridges minor flatness issues but offers minimal moisture protection on its own.
Use standard foam over plywood subfloors above grade — bedrooms upstairs, living rooms over crawlspaces with dry access. Skip it for any concrete installation; the lack of vapor barrier will cause problems within a year.
Foam with Vapor Barrier
The same foam laminated with a polyethylene moisture barrier on one side. Around $0.30 to $0.50 per square foot. The barrier faces down toward the subfloor and seams overlap with built-in tape strips.
This is the right choice over concrete slabs, basement floors, and anywhere humidity rises above 60 percent seasonally. Look for a perm rating below 0.10 — anything higher will pass too much moisture into the laminate over time.
Cork Underlayment
Natural cork sheets at 3 mm to 6 mm thickness deliver superior sound control and a slightly springy feel. Cost runs $0.50 to $1.50 per square foot.
Cork is the best acoustic choice for upstairs bedrooms, condos with HOA noise rules, and home theaters. It does not include a vapor barrier, so pair it with a separate poly sheet over concrete subfloors. Cork is also more dimensionally stable than foam, reducing edge gapping in older homes with humidity swings.
Felt Underlayment
Recycled fiber felt at 3 mm thickness sits between foam and cork in performance and price. Around $0.40 to $0.80 per square foot.
Felt is denser than foam, offering better impact insulation and a quieter feel underfoot. It does not include a vapor barrier in basic versions. Use felt for second-story bedrooms and apartments where sound reduction matters but cork stretches the budget.
Premium Combination Underlayment
Multi-layer products like Quietwalk Plus combine fiber, foam, and a vapor retarder in one roll. Cost climbs to $0.70 to $1.50 per square foot but delivers acoustic, moisture, and cushioning benefits in one product.
This is the safe choice for any installation where you want to skip product-matching headaches. The IIC and STC sound ratings printed on the package help condo owners meet HOA requirements without separate testing.
Subfloor-Specific Recommendations
Plywood or OSB Above Grade
Standard 2 mm or 3 mm foam works fine. Add felt or cork if sound is a concern. No vapor barrier needed unless you live in extreme humidity zones.
Concrete Slab
Always use foam with attached vapor barrier or a combination underlayment with a moisture rating. Run a calcium chloride moisture test first — readings above 3 pounds per 1,000 sq ft per 24 hours require additional waterproofing.
Existing Vinyl or Tile
Standard foam works if the existing surface is flat and intact. Inspect for cracks, lifting tiles, or hollow spots and repair before installation. Skip felt over uneven existing tile because the bumps will telegraph through.
Radiant Heat Subfloor
Use only underlayment rated for radiant heat with a low thermal resistance value (R-value below 0.25). Cork and dense foam often fail this test — buy a product specifically labeled as radiant-compatible.
Built-In Pad on Laminate Planks
Some premium laminates ship with attached underlayment pre-glued to the bottom. If you choose one of these products, you only need a separate vapor barrier over concrete — no additional underlayment.
Stacking foam on top of an attached pad creates too much cushioning and can cause click joints to flex apart over time. Read the manufacturer instructions before assuming you need a second layer.
What Not to Use
- Carpet padding — too soft, causes click joint failure
- Plastic sheeting alone — no cushioning, traps moisture in pockets
- Tar paper — incompatible with most laminate adhesives in seams
- Multiple foam layers — exceeds laminate manufacturer specifications
- Damaged or wrinkled rolls — every imperfection telegraphs through
Installation Tips
Roll out underlayment perpendicular to your laminate planks. Butt seams together — never overlap, even on foam without a barrier. Tape seams with manufacturer-supplied tape or quality polyethylene seam tape.
For vapor barriers, run the plastic 4 inches up each wall and trim flush after baseboard installation. Overlap seams 6 to 8 inches and tape thoroughly. A tear or gap defeats the entire moisture-blocking purpose.
Acclimate both the underlayment and laminate in the room for 48 hours before installation. Cold or damp underlayment expands after install, creating bumps that show up months later.
Cost vs Performance Summary
- Standard foam — $0.10-$0.30 per sq ft, basic cushioning only
- Foam with vapor barrier — $0.30-$0.50, required over concrete
- Felt — $0.40-$0.80, better sound and impact
- Cork — $0.50-$1.50, premium acoustics and stability
- Combination products — $0.70-$1.50, all-in-one solutions
Underlayment is one of the few areas where spending an extra $100 on a 500-square-foot project meaningfully improves daily comfort and floor longevity. Pick the right product for your specific subfloor, and the question of what do you put under laminate flooring turns into the foundation of a quiet, stable installation that lasts 20-plus years.
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