Best Underlayment for Hardwood Floors: A Complete Buyer’s Guide

Choosing the right underlayment for hardwood floors is one of those decisions that is invisible once the floor is installed — but makes a dramatic difference in how the floor sounds, feels, and performs over its lifetime. The correct underlayment reduces noise, smooths minor subfloor imperfections, provides a moisture barrier where needed, and can even improve thermal insulation.

The wrong underlayment — or skipping it entirely when it is needed — leads to hollow-sounding floors, moisture damage, and premature wear. This guide covers every underlayment type, matched to the three primary hardwood installation methods, so you can make the right choice for your project.

Underlayment by Installation Method

The type of underlayment you need depends entirely on how your hardwood floor is being installed. The three main methods — nail-down, floating, and glue-down — each have different underlayment requirements.

Underlayment for Nail-Down Hardwood

Nail-down installation is the traditional method for solid hardwood over plywood or OSB subfloors. The underlayment in this case is thin and serves two purposes: it provides a slip sheet between the hardwood and subfloor (reducing squeaks) and offers minor moisture protection.

Rosin Paper

Rosin paper is the classic, time-tested underlayment for nail-down hardwood. It is a heavy-duty craft paper treated with rosin (pine resin) for moisture resistance. Rosin paper lies flat, does not bunch up during installation, and prevents the hardwood from directly contacting the subfloor — which reduces squeaking caused by wood-on-wood friction.

• Thickness: Very thin (single layer)
• Cost: $0.05-$0.10 per sq ft
• Pros: Inexpensive, lies flat, reduces squeaks, easy to install
• Cons: Minimal moisture protection, no sound reduction
• Best for: Standard nail-down installation over plywood subfloor

Felt Paper (15 lb or 30 lb)

Asphalt-saturated felt paper (also called tar paper or builder’s felt) is the other traditional underlayment for nail-down hardwood. It provides slightly better moisture resistance than rosin paper and a modest level of sound dampening due to its denser composition.

• Thickness: 15 lb (~1/16 inch) or 30 lb (~1/8 inch)
• Cost: $0.08-$0.15 per sq ft
• Pros: Better moisture resistance than rosin paper, some sound dampening, widely available
• Cons: Can wrinkle if not laid carefully, slight odor during installation, minimal sound reduction compared to floating underlayments
• Best for: Nail-down installation where moderate moisture protection is desired

For most standard nail-down hardwood flooring installations over plywood subfloors, either rosin paper or 15 lb felt paper is an appropriate and cost-effective choice. The differences between them are subtle, and both are accepted by virtually all hardwood flooring manufacturers.

Underlayment for Floating Hardwood

Floating installation — where engineered hardwood planks click together and sit on top of the subfloor without nails or glue — requires a more substantial underlayment. The underlayment serves as the cushioning layer between the floor and the subfloor, and it dramatically affects how the floor sounds and feels underfoot.

Cork Underlayment

Cork is widely considered the premium underlayment for floating hardwood floors. It offers the best combination of sound reduction, comfort, and moisture resistance of any standard underlayment material.

• Thickness: 3mm or 6mm
• Cost: $0.50-$1.25 per sq ft
• Sound reduction (IIC): 15-22 points improvement
• Pros: Excellent sound absorption (both impact and airborne), natural antimicrobial properties, comfortable underfoot, eco-friendly, good thermal insulation
• Cons: Higher cost, requires separate vapor barrier over concrete, can compress slightly over time under heavy loads
• Best for: Multi-story buildings, condos (often required by HOA), bedrooms, living areas where quiet is important

Cork underlayment is the go-to choice when noise reduction is a priority. In condominiums and multi-story homes, building codes and HOA regulations often specify a minimum IIC (Impact Insulation Class) rating of 50-60 — cork underlayment helps meet these requirements.

Foam Underlayment

Closed-cell foam (polyethylene or polypropylene) underlayment is the most common and affordable option for floating floors. It provides adequate cushioning and sound reduction for most residential applications.

• Thickness: 2mm-3mm (standard) or 1.5mm (thin profile)
• Cost: $0.15-$0.40 per sq ft
• Sound reduction (IIC): 8-15 points improvement
• Pros: Affordable, easy to install, good moisture barrier (closed-cell), lightweight
• Cons: Less sound reduction than cork, can compress and degrade over time, lower quality products may off-gas
• Best for: Budget-conscious floating installations, single-story homes, areas where noise is not a major concern

Combination Underlayment (Foam + Vapor Barrier)

Many modern underlayments combine a foam or cork cushion layer with an attached polyethylene vapor barrier. These 2-in-1 or 3-in-1 products simplify installation by eliminating the need for a separate moisture barrier sheet. Popular products include:

• QuietWalk: Recycled fiber pad with attached vapor barrier — excellent sound ratings and moisture protection
• Floor Muffler: Closed-cell cross-linked foam with integrated vapor barrier — outstanding impact sound reduction
• Roberts Super Felt: Recycled fiber with attached film — good balance of cost and performance

Combination underlayments typically cost $0.25-$0.75 per square foot and offer the convenience of single-layer installation with solid performance across all metrics.

Underlayment for Glue-Down Hardwood

Glue-down engineered hardwood is adhered directly to the subfloor with flooring adhesive. In most cases, no separate underlayment is used — the adhesive bond itself provides the connection, and adding a cushion layer would compromise the bond.

However, two scenarios require additional attention with glue-down installations:

• Moisture protection over concrete: Apply a moisture barrier primer (like Bostik MVP4 or Mapei Planiseal VS) directly to the concrete before installing. This seals the concrete surface and prevents moisture vapor from reaching the hardwood.
• Sound reduction needed: Some acoustic mat products (like Proflex 90 or Regupol) can be installed under glue-down hardwood. The adhesive is applied on top of the mat, and the hardwood is glued to the mat surface. This is more complex and expensive but adds significant noise reduction for multi-story applications.

Moisture Barrier: When You Need One

Concrete subfloors are the most critical case for moisture protection. Concrete is porous and wicks moisture from the ground below, even when it appears dry. This moisture vapor can destroy hardwood floors from beneath. Always test concrete moisture levels before installation using a calcium chloride test (ASTM F1869) or relative humidity probe (ASTM F2170). Acceptable levels are below 3 lbs per 1,000 sq ft per 24 hours (calcium chloride) or below 75% RH (humidity probe). Learn more about subfloor preparation in our hardwood floor installation guide.

Sound Reduction Comparison

Sound performance is measured by two ratings:

• IIC (Impact Insulation Class): Measures how well the floor/underlayment assembly blocks impact sounds (footsteps, dropped objects) from being heard in the room below. Higher is better.
• STC (Sound Transmission Class): Measures how well airborne sound (voices, music, TV) is blocked. Higher is better.

Thickness Guide

Underlayment thickness is not a “more is better” situation. Too-thick underlayment under floating floors creates excessive flex that can damage click-lock joints and cause planks to separate over time. Follow these guidelines:

• Nail-down hardwood: Use the thinnest option (rosin paper or 15 lb felt). Thick underlayment interferes with nail penetration and holding power.
• Floating hardwood: 2mm to 3mm is the standard range. Use 3mm for better sound performance. Only go to 6mm if specifically recommended by the flooring manufacturer and your sound reduction needs require it.
• Glue-down hardwood: No underlayment (or acoustic mat per manufacturer specs).

Always check the hardwood flooring manufacturer’s installation instructions for approved underlayment types and thicknesses. Using an unapproved underlayment can void the flooring warranty. For more on underlayment options across all flooring types, visit our dedicated guide.

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