Best Underlayment for Hardwood Floors: What Actually Works (2026)

You can pick the most beautiful hardwood floor on the market and still end up with a disaster if you get the underlayment wrong. Cupped boards, failed click-locks, squeaky floors, mould under the planks: every one of those problems can trace back to a bad underlayment choice. Yet most guides treat underlayment as an afterthought, a single line at the end of an install checklist.

This guide does the opposite. We're going to break down the best underlayment for hardwood floors by subfloor type, installation method, and use case, so you know exactly what to buy before the flooring truck shows up.

Why Underlayment Choice Actually Matters

Underlayment does four things: it controls moisture movement, it dampens sound, it cushions the floor slightly, and it bridges minor subfloor imperfections. The problem is that optimizing for one function can actively hurt another. A thick, cushy foam feels great underfoot but compresses under load, and that compression can cause click-lock joints to separate over time. A rigid felt pad gives you almost no cushion but keeps a floating floor locked tight.

The National Wood Flooring Association (NWFA) underlayment guidelines are clear on this: floating floor underlayment must have published compression resistance and density values that meet the flooring manufacturer's minimum requirements. That spec exists for a reason. When underlayment compresses unevenly, it puts lateral stress on your locking system and shortens the floor's life.

So before we look at specific products, let's understand the four main underlayment types and what each one is actually good for.

The Four Main Types of Hardwood Underlayment

1. Foam Underlayment

Foam is the most common underlayment sold in flooring stores, and it's also the most commonly misused. Standard polyethylene foam is cheap (roughly $0.30 to $0.50 per square foot), easy to roll out, and adds a small amount of sound buffering. It compresses easily under weight, which makes it feel soft at first, and that softness is exactly the problem for floating hardwood.

For a nail-down or glue-down hardwood installation, foam underlayment is not appropriate at all. It doesn't bond, it shifts, and it adds no structural value to an adhered system. For a floating floor, you can use foam, but you need to verify the density and compression resistance match your flooring manufacturer's spec. If the spec sheet says maximum 3mm underlayment, do not go thicker. The joint failure risk is real.

Foam does make sense for floating hardwood installations in basements where the subfloor is concrete and you're adding a separate vapour barrier sheet underneath the foam. In that configuration, the foam adds a touch of acoustic dampening on top of the vapour control layer.

Best for: Budget floating installs on concrete with a separate vapour barrier below, or above-grade floating floors on plywood where moisture is not a concern.

2. Cork Underlayment

Cork is the acoustic performer of the underlayment world. It's a natural material, denser and more dimensionally stable than foam, and it compresses much less under load. For floating hardwood floors, cork in the 2mm to 3mm range gives you meaningful sound reduction without the joint-stress risk that comes with over-thick foam. BuildDirect Canada's underlayment guide also recommends semi-permeable products for plywood subfloors and impermeable products for concrete, a distinction that maps directly to what we cover throughout this guide.

Cork is particularly relevant for anyone living in a condo or multi-unit building where you need to meet IIC and STC requirements. We'll cover those acoustic ratings in detail below, but the short version is: cork regularly outperforms foam in independent acoustic tests, and some building codes in Canada require IIC ratings of 50 or higher for any floating floor installation over a shared ceiling assembly.

Cork does not function as a vapour barrier. Over concrete, you still need a Class I vapour retarder below the cork, either a separate 6-mil poly sheet or a combo product. Over plywood in a conditioned space, the NWFA says a vapour retarder is often not required, so cork alone can be sufficient.

Best for: Condos, multi-story homes, and any situation where sound transmission is a priority. Pairs well with floating installs.

3. Felt Underlayment

Felt (asphalt-saturated felt paper, sometimes called roofing felt or tar paper) has been used under hardwood floors for over a century. The NWFA's own moisture guidelines list it as an acceptable Class II multi-layer system component when installed over concrete subfloors, and it's the traditional choice under nail-down solid hardwood over plywood.

Felt is semi-permeable, which is actually a benefit over plywood subfloors. Wood subfloors need to breathe. A completely impermeable barrier between two wood layers can trap moisture and cause mould, rot, or corrosion of metal fasteners. Felt allows controlled vapour diffusion while still providing a modest buffer against incidental moisture.

Felt adds minimal thickness (usually 1mm or less), which means it doesn't interfere with nail-down fastener penetration into the subfloor. That's why traditional installers have used it for decades under nail-down systems.

Felt is not a good fit for floating installations because it offers almost no compression resistance or sound isolation, and it can shift without adhesion. For nail-down or staple-down installs, it remains one of the most reliable and cost-effective choices available.

Best for: Nail-down hardwood over plywood subfloors. An affordable, traditional option with a long track record.

4. Vapour Barrier and Combo Products

Combo underlayments combine a physical cushioning layer (foam, cork, or fibre) with an integrated vapour barrier. The vapour barrier is typically a polyethylene film laminated to the underside of the pad. These products are the most practical option for floating hardwood over concrete because they solve both the moisture control and the cushioning requirement in a single install step.

EasiKlip's Vapour Shield Premium Floor Underlayment is a good example of this category. It's engineered for floating solid and engineered hardwood, with a compression-tested foam layer bonded to a Class I vapour barrier film. Because the barrier is factory-integrated, you don't have to manage overlapping and taping a separate poly sheet, and you eliminate the risk of punctures or gaps that can happen when the barrier and the pad are separate products installed sequentially.

The critical spec to check with any combo product is the total thickness. Many combo products run 3mm to 5mm thick. Over 3mm total, you risk forcing floating planks out of tolerance at the joints. Confirm the maximum allowable underlayment thickness in your flooring manufacturer's installation guide before purchasing.

Best for: Floating hardwood over concrete. Also appropriate for floating installs over plywood where you want a single-step moisture and cushioning solution.

Concrete vs. Plywood Subfloor: The Decision That Changes Everything

Your subfloor type is the single most important variable in picking the right underlayment. The concrete vs. plywood question determines your moisture exposure, your installation method, and which underlayment products are even on the table.

Concrete Subfloors

Concrete is porous. Even a slab that looks and feels dry will transmit vapour upward year-round, especially below grade. The NWFA guidelines state that a Class I impermeable vapour retarder is always recommended for on- and below-grade concrete applications, because slab moisture conditions change seasonally and a sub-slab barrier can degrade over time.

Practically speaking, this means: if your subfloor is concrete, assume you need a vapour barrier. Don't test, shrug, and skip it. The consequences of moisture under hardwood are warping, cupping, mould, and a complete redo. We cover the full moisture testing protocol in our guide to when and why you need a moisture barrier for wood floors.

For floating installs over concrete, use a combo underlayment with an integrated vapour barrier (like Vapour Shield), or use a 6-mil poly sheet lapped up the walls with taped seams, followed by a separate underlayment pad. For glue-down installs over concrete, use a vapour-barrier adhesive system compatible with your wood flooring adhesive. Do not put a foam underlayment pad under a glue-down floor on concrete. The adhesive needs to bond directly to the substrate.

Our full guide to installing wood flooring over concrete goes through moisture testing and subfloor prep in detail if you want the step-by-step.

Plywood Subfloors

Plywood over a conditioned space (heated basement below, normal living area, etc.) is the most forgiving underlayment situation. The NWFA says a vapour retarder is not required when the space below is maintained at the same temperature and humidity as the space above, unless the flooring manufacturer says otherwise.

For nail-down installs over plywood, felt paper is the traditional and reliable choice. For floating installs over plywood, a cork or foam pad in the 2mm to 3mm range gives you cushion and minor sound buffering without a vapour barrier requirement. If your plywood is over an unconditioned crawlspace or the subfloor has a history of moisture, step up to a Class II semi-permeable retarder below your underlayment pad.

Plywood quality matters here too. A poorly prepared or uneven plywood subfloor will transfer its imperfections through any underlayment into your finished floor. Before you worry about underlayment type, make sure the subfloor is flat, clean, and structurally sound. Our subfloor prep guide for concrete, plywood, and OSB walks through the process. If levelling is an issue, read our post on how to level a subfloor for hardwood floors before proceeding.

Thickness Matters: Why Thicker Is NOT Always Better

This is the most common underlayment mistake DIYers make. It feels logical: more cushion equals more comfort, more protection, better result. For hardwood, especially floating hardwood, that logic breaks down fast.

Floating hardwood systems lock at the edges of each plank. When you walk on a floating floor, the planks flex slightly under load. If the underlayment is too thick, that flex increases, and the locking mechanism takes on stress it wasn't designed to handle. The joints gradually weaken, gaps open up, and in worst-case scenarios the click-lock tabs crack.

Most floating hardwood manufacturers specify a maximum underlayment thickness between 2mm and 3mm. Some premium click-lock systems allow up to 4mm. Almost none allow 5mm or more. Check your flooring's installation guide, find the underlayment spec, and stay within it.

For nail-down systems, thickness is less critical because the nails penetrate through the underlayment into the subfloor. The concern there is that an extremely thick underlayment can reduce fastener penetration depth, which weakens the mechanical hold. Felt at 1mm or less keeps the fasteners at full depth.

For glue-down systems, the adhesive needs substrate contact. No underlayment pad goes between a glue-down floor and a concrete or plywood subfloor. The only product that belongs there is a moisture-control adhesive with built-in barrier properties, applied directly to the slab. Our post on real hardwood without nails, glue, or sanding covers alternative install methods in more detail.

IIC and STC Acoustic Ratings Explained Simply

If you live in a condo, apartment building, or any multi-storey structure, acoustic ratings are not optional knowledge. Many buildings have minimum acoustic performance requirements written into strata bylaws or local building codes, and the underlayment you choose is a major variable in whether your floor assembly meets those thresholds.

Two ratings matter: IIC and STC.

IIC (Impact Insulation Class) measures how well a floor assembly blocks impact sounds: footsteps, dropped objects, anything that creates vibration through the structure. A higher IIC score means less impact noise transmitted to the unit below. Most condo strata rules in Canada require an IIC of 50 or higher. Some require 55.

STC (Sound Transmission Class) measures airborne sound: voices, music, television. STC ratings for floor assemblies are typically lower than their IIC ratings because flooring is primarily a structural surface, not a wall. A minimum STC of 50 is a common baseline requirement.

According to the STC and IIC Ratings catalog published by the Technical Standards and Instruction Bureau, cork underlayment in a floating floor assembly consistently produces IIC ratings in the 50-60 range depending on the floor/ceiling assembly type. Standard foam pads without acoustic enhancement often score in the low-to-mid 40s in the same assembly configurations.

The key word in all of this is "assembly." Your underlayment doesn't produce an IIC score in isolation. The score comes from the whole system: the flooring planks, the underlayment, the subfloor, the ceiling below. When you're sourcing underlayment for a condo or multi-unit building, ask your underlayment supplier for a published IIC/STC test result from an assembly that resembles your actual floor construction, not just a standalone material rating.

The NWFA guidelines also note that you should never nail through an acoustical underlayment because doing so can compromise the specified IIC and STC ratings. That's another reason nail-down installs don't use thick acoustic pads.

Vapour Barrier: Built-In vs. Separate Sheet

Once you've decided you need moisture control (and over concrete, you do), you have two practical paths: a combo underlayment with an integrated vapour barrier, or a separate 6-mil polyethylene sheet installed first, followed by a standalone underlayment pad on top.

Here's when each approach makes sense:

Integrated combo (like Vapour Shield): Ideal for DIYers. Fewer materials to manage, one step instead of two, and no risk of the separate poly sheet sliding out of position while you're laying the flooring. The barrier is factory-bonded to the pad, so seams are managed with the manufacturer's seaming tape and the product installs consistently. For a typical floating hardwood install over concrete, this is the fastest and most foolproof approach.

Separate 6-mil poly sheet plus standalone pad: Better when you need precise control over each layer's specification. For example, if your flooring manufacturer requires a specific foam density and a separate ASTM-tested vapour barrier rating, you may need to source them independently. Commercial installs or large-format projects sometimes have this requirement. The separate sheet needs to be lapped 6 to 8 inches up the walls, with all seams overlapped and taped with impermeable moisture-control tape.

One important nuance: over plywood subfloors, you almost never want a fully impermeable vapour barrier. A Class I (completely impermeable) barrier between two wood layers traps any moisture that gets in, which creates exactly the mould environment you were trying to prevent. Over plywood, use semi-permeable (Class II) products that allow the wood to breathe, or use no barrier at all if the space below is conditioned.

Underlayment for Each Installation Method

The install method is a hard constraint on underlayment type. Here's the direct summary:

• Floating: Use a compression-resistant foam, cork, or combo pad rated to 3mm or less (or whatever your flooring manufacturer specifies). Over concrete, ensure a Class I vapour barrier is present, either integrated or separate. Expansion gaps are critical with floating installs; our post on whether hardwood expansion gaps are really necessary explains why.
• Nail-down or staple-down: Use asphalt-saturated felt paper (15-lb felt). It's thin, semi-permeable over plywood, and doesn't reduce fastener penetration depth. Do not nail through thick acoustic pads.
• Glue-down: No pad underlayment between the floor and the subfloor. Use a vapour-control adhesive system over concrete. The adhesive is the only product that goes between the plank and the concrete.

If you're still deciding which method fits your project, our full guide on floating vs. nail-down vs. glue-down walks through each scenario.

Underlayment Comparison Table: Foam vs. Cork vs. Felt vs. Combo

The Myth-Busting Section: Common Underlayment Misconceptions

Myth 1: "Any underlayment works for any hardwood installation."

False. This is the most dangerous myth in the underlayment category. Glue-down installs require no pad underlayment. Nail-down installs require thin, semi-permeable felt. Floating installs need compression-tested, manufacturer-approved products within a maximum thickness spec. Using foam underlayment under a glue-down floor prevents adhesion. Using thick foam under a floating floor stresses the click-lock joints. These are not small mistakes. They cause failed installations.

Myth 2: "Thicker underlayment means a softer, better-feeling floor."

Partly true, mostly harmful for hardwood. Thicker underlayment compresses more under dynamic load. That compression translates into micro-movement at every plank joint in a floating floor. Over months and years, that micro-movement breaks down the locking mechanism. Your floor starts to feel and sound hollow, gaps open between planks, and there's no repair other than a full reinstall. The floor feels softer because it's flexing when it shouldn't be.

Myth 3: "You don't need a vapour barrier on concrete if the concrete passes the moisture test."

False. The NWFA is explicit: moisture test results reflect conditions at the time of testing, not permanent conditions. Seasonal moisture changes, temperature swings, and long-term degradation of any sub-slab barrier all affect moisture transmission over time. Over on- and below-grade concrete, a Class I impermeable vapour retarder is always recommended regardless of test results at install.

Myth 4: "Underlayment isn't necessary if the subfloor is perfectly flat."

Depends on the installation method. A perfectly flat plywood subfloor doesn't automatically eliminate the need for underlayment. Nail-down installs still benefit from felt for its semi-permeable moisture buffering. Floating installs over concrete still need moisture control regardless of flatness. And in a condo, your acoustic requirements may mandate an underlayment even if the subfloor prep is flawless.

Myth 5: "The IIC rating printed on the underlayment package applies to your floor."

Usually false. An IIC rating is always assembly-specific. The number on the package was tested in a specific floor/ceiling configuration that likely differs from yours. Ask for a published test from an assembly resembling your actual construction, or request an engineering review if you have a mandated strata requirement.

What Underlayment Actually Costs: The $0.30 to $1.50/sq ft Breakdown

Underlayment adds between $0.30 and $1.50 per square foot to your project, depending on product type. For a 500-square-foot room, that's $150 to $750. Is it worth it?

Yes, and here's why the comparison makes itself: a basic moisture barrier failure on a concrete subfloor costs $3 to $8 per square foot to replace the damaged flooring, plus demo costs, plus any structural remediation for mould. On a 500-square-foot floor, that's $1,500 to $4,000 in remediation. The $250 you saved by skipping the combo underlayment is gone ten times over.

The cost-per-square-foot view also makes it easier to weigh acoustic upgrades. Going from a $0.40 foam to a $0.85 cork pad costs $225 more on a 500-square-foot floor. If that $225 upgrade means your floor passes your strata's IIC requirement and avoids a forced reinstall, it's not a cost, it's an insurance policy.

The Right Underlayment for Floating Hardwood Over Concrete

Let's make this completely concrete (yes, the pun). If you're putting floating hardwood in a basement or over a concrete slab anywhere in the house, here is the exact product category you need:

A combo underlayment with a factory-integrated Class I vapour barrier, rated to the maximum thickness specified by your flooring manufacturer, with published compression resistance values. EasiKlip's Vapour Shield Premium Floor Underlayment is built for exactly this scenario. You can browse the full range of installation materials and accessories in the EasiKlip DIY hardwood floor store.

For more on the concrete-specific install process, including moisture testing and vapour barrier prep before you lay your underlayment, see our in-depth guide to installing wood flooring over concrete. And if you're in a basement specifically, our floating hardwood for basements guide covers everything from moisture management to species selection.

Conclusion: Match Underlayment to Your Installation, Not Your Budget

The best underlayment for hardwood floors is not the most expensive one, and it's not the thickest one. It's the one that matches your subfloor type, your installation method, and your acoustic requirements.

To recap the key decisions:

• Concrete subfloor: Class I vapour barrier required, always. Use a combo product or a separate poly sheet plus a pad.
• Plywood subfloor over conditioned space: felt for nail-down, foam or cork for floating, semi-permeable or no barrier needed.
• Floating install: Stay within 3mm thickness unless your manufacturer specifies otherwise. Compression resistance is the spec that matters.
• Glue-down install: No pad underlayment. Use a moisture-control adhesive system directly on the subfloor.
• Condo or multi-unit building: Cork or premium combo for acoustic ratings. Verify IIC and STC from a comparable assembly, not the package label.

Get those decisions right, and the underlayment becomes invisible: exactly what it should be.

Frequently Asked Questions

Do I need underlayment under hardwood floors if my subfloor is perfectly level?

It depends on your install method. Nail-down installs over plywood still benefit from felt paper for its semi-permeable moisture buffering. Floating installs still need underlayment for compression resistance and, if over concrete, moisture control. A level subfloor is a great starting point; it doesn't replace underlayment's other functions. See our subfloor prep guide for what to check before you install.

Can I use the same underlayment for floating and glue-down hardwood?

No. Floating installs use a pad underlayment (foam, cork, or combo). Glue-down installs bond directly to the subfloor, so no pad goes between the plank and the substrate. Using a foam pad under a glue-down floor prevents the adhesive from bonding and the floor will fail. The installation method determines the underlayment category.

What is the maximum underlayment thickness for a floating hardwood floor?

Most floating hardwood manufacturers specify a maximum of 3mm, though some premium systems allow up to 4mm. Anything thicker risks increasing joint flex to the point where click-lock tabs crack or gaps open. Always check the specification in your flooring manufacturer's installation guide before purchasing underlayment.

Does underlayment replace a vapour barrier over concrete?

Not unless the underlayment includes a factory-integrated Class I vapour barrier. A standard foam or cork pad is not a vapour barrier. Over concrete, you need either a combo product with an integrated barrier or a separate 6-mil polyethylene sheet installed below the pad, with seams overlapped and taped.

What IIC rating do I need for a condo installation?

Most Canadian condo strata bylaws require a minimum IIC of 50, and some require 55. Check your building's specific requirements before selecting materials. Cork underlayment in a typical floating floor assembly typically achieves IIC 50 to 60, depending on the full floor/ceiling assembly. Request a published test report from an assembly resembling your floor construction.

Is cork underlayment worth the extra cost over foam?

For condos or any situation with acoustic requirements, yes. Cork's higher density means less compression under load (better for joint longevity) and meaningfully better IIC ratings than standard foam. The cost premium is typically $0.25 to $0.55 per square foot. On a 500-square-foot room, that's $125 to $275 extra. If it keeps you compliant with strata rules and avoids a forced reinstall, the math is straightforward.

Can I add underlayment under an existing hardwood floor that is squeaking?

Not without pulling up the floor. Underlayment is installed before the flooring goes down, and there's no effective way to insert it after installation. If your floor is squeaking, the cause is usually subfloor movement, inadequate fasteners, or a moisture issue, not missing underlayment. Our guide on subfloor levelling may help identify the root cause.

Do I need underlayment for a nail-down hardwood floor over plywood?

Yes, felt paper (15-lb asphalt-saturated felt) is standard for nail-down over plywood. It's semi-permeable, which means it allows the two wood layers to breathe without trapping moisture between them. It's thin enough that it doesn't reduce fastener penetration depth, and it provides a minor buffer against incidental moisture. The NWFA underlayment guidelines describe felt as an appropriate Class II multi-layer system component for wood subfloor applications.