So, you are trying to figure out which underlayment you actually need for sound and moisture, without wasting money or wrecking your floor.
You need an underlayment that matches your floor type, your subfloor, and your building (multi‑family vs single home), with a balance of sound ratings (STC/IIC) and moisture protection (vapor barrier or not).

Most people get this wrong because underlayment looks like a boring roll of foam or felt. But that “boring” layer is what protects your floor from squeaks, mold, and neighbor complaints. If you pick the wrong one, problems show up slowly. Humidity warps your planks. Impact noise travels through the structure. Your nice new floor feels cheap and hollow. All because of a 2 mm layer you barely see.

Here is what you need to keep in mind before you click “buy” or say yes to whatever the installer suggests.

• Your floor type decides about 50% of the underlayment choice (laminate vs vinyl vs engineered wood vs tile).
• Your subfloor (concrete vs wood) decides if you need a vapor barrier.
• Sound control is about two ratings: STC (airborne) and IIC (impact).
• Multi‑family buildings often require minimum STC/IIC ratings by code or HOA rules.
• Too thick or too soft underlayment can void your flooring warranty.
• Moisture under a floating floor is more dangerous than most people think.
• Some floors come with pre‑attached underlayment; doubling up can cause problems.
• Rubber usually wins on sound, foam is budget‑friendly, cork is the green middle ground, felt is a favorite under wood.

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What underlayment actually does (beyond just “padding”)

So you are looking at underlayment rolls and thinking it is just a cushion. It is not. A good underlayment is doing 4 different jobs at once:

• Sound control
• Moisture control
• Minor leveling and support
• Comfort and feel underfoot

Let us break those down quickly.

1. Sound control basics: STC and IIC

If you care about noise, two numbers matter:

• STC (Sound Transmission Class): how well the floor assembly blocks airborne noise like voices, TV, and music.
• IIC (Impact Insulation Class): how well it reduces impact noise like footsteps, chairs moving, or dropped objects.

Higher numbers are better. In condos and apartments, you often see rules like:

• Minimum STC 50
• Minimum IIC 50

Building code targets around 50. High‑end projects aim for 55-60. The catch: those ratings are for the whole assembly (ceiling + structure + underlayment + floor), not just the underlayment.

Still, underlayment choice can swing IIC by 5-10 points, which is the difference between “I can hear every step” and “I know someone is upstairs, but it is fine.”

Underlayment product pages usually list something like:

• STC: 66 over 6″ concrete
• IIC: 71 over 6″ concrete

Always check:

• What floor system they tested with (laminate, vinyl, wood).
• What subfloor (concrete slab vs wood frame).
• If they used a drop ceiling or resilient channels.

Because numbers can look similar, but test conditions change everything.

If you live over someone else, treat IIC like non‑negotiable. It is what stops your footsteps from becoming their problem.

2. Moisture control: vapor barrier vs breathable

This is where you can cause long‑term damage quietly.

You need to ask one basic question:

• Is moisture coming up from below my floor?

If your answer is yes (or even “maybe”), then:

• Concrete slab: you almost always need a vapor barrier.
• Basement: assume moisture risk.
• Over crawlspace: check whether the crawlspace is sealed and vented, but treat it with caution.

Vapor barrier underlayments usually have:

• Poly film attached, or
• Integrated waterproof surface

These are designed to slow or block moisture movement up into your floor.

But there is a twist.

Wood and some engineered floors want to breathe. Locking moisture under them with the wrong barrier can backfire.

So you need to match:

• Floor type
• Subfloor type
• Manufacturer instructions

Do not guess here. Moisture problems take months or years to show, and then it is expensive.

3. Minor leveling and support

Underlayment is not a replacement for real subfloor prep. It will not fix big humps or dips.

But it can help with:

• Small variations (like 1-2 mm)
• Bridge over minor seams
• Support floating floors evenly to reduce movement

Certain materials do this better:

• Rubber and high‑density foam give good support.
• Cheap low‑density foam compresses and can lead to squishiness and joint failure.

If you have more than about 3/16″ variation over 10 feet (check your floor specs), underlayment is not the fix. You need patching or self‑leveling compound first.

4. Comfort and feel underfoot

The “feel” of your floor is partly the underlayment. That includes:

• How solid it feels when you walk
• How hollow it sounds
• How much it flexes when you step

Too soft:

• Floating floors can move and creak
• Click joints can break over time

Too hard:

• More impact noise
• Less comfortable, especially with hard shoes

The goal is a balance. Slight give, strong support.

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Main underlayment types for sound and moisture

Let us look at the most common choices. Think of this like a menu, but you need the right combo for your exact “dish”: floor + subfloor + building.

Quick comparison of common underlayment types

Material	Sound (IIC/STC)	Moisture behavior	Typical thickness	Common uses
Basic foam	Low to medium	No real moisture barrier	1-3 mm	Laminate over wood in single homes
Foam with vapor barrier	Medium	Built‑in film layer blocks moisture	2-3 mm	Laminate over concrete slabs
Rubber	High (especially IIC)	Often moisture resistant, some with full barrier	2-12 mm	Condos, multi‑family, gyms, commercial spaces
Cork	Medium to high	Breathable; needs extra barrier over concrete	2-6 mm	Engineered wood, laminate over wood subfloors
Felt / fiber	Medium to high	Can be breathable or with barrier film	2-6 mm	Engineered wood, nail‑down, some floating floors
Combination (multi‑layer)	Medium to high	Usually includes integrated vapor barrier	2-4 mm	Premium laminate, vinyl in condos

Do not focus only on thickness. High density with 2 mm can outperform spongy 5 mm for both sound and durability.

Foam underlayment

Foam is the starter option for many floors. It comes in a few flavors.

• Standard foam (no barrier)
• Foam with attached vapor barrier film
• High‑density or “premium” foam

Pros:

• Low cost
• Easy to install (light, cuts with a knife)
• Works with many laminates

Cons:

• Basic foam has limited sound control
• Cheap foam compresses over time
• Poor choice for serious multi‑family sound rules

Best for:

• Laminate over wood subfloor, in houses or upper levels where noise rules are mild.
• Budget projects where sound is “nice to have” but not strict.

Rubber underlayment

Rubber underlayment is often the top performer when sound is the priority. It is heavy and dense, which is exactly what you want for noise.

Typical thickness ranges:

• 2 mm to 12 mm

The thicker products usually exist for gyms or special builds, but for residential floors you often see 2-5 mm.

Pros:

• Very strong impact sound reduction (high IIC)
• Good airborne sound control as part of a system
• Great durability, resists compression
• Some products include integrated vapor barrier

Cons:

• More expensive than foam
• Heavier and a bit harder to cut and handle
• Can have odor at first from some brands

Best for:

• Condos and apartments where your HOA or building has strict sound ratings.
• Floors over concrete that need both IIC performance and some moisture resistance.
• Engineered wood or laminate where the manufacturer allows rubber.

If you are trying to get from IIC 45 to IIC 50+ over a slab, rubber often gets you there.

Cork underlayment

Cork is popular with people who want a natural material and decent sound performance.

Pros:

• Good acoustic performance in the medium thicknesses (3-6 mm)
• Resilient and can last a long time
• Stable and supportive under floating floors

Cons:

• Not a vapor barrier by itself
• Can absorb moisture and grow mold if exposed
• Usually costs more than basic foam

Best for:

• Engineered wood or laminate over wood subfloor.
• Situations where you want something more natural than rubber or foam.

Over concrete, cork usually needs a separate vapor barrier (like 6 mil poly) under it. Skipping that can be a slow mistake.

Felt and fiber underlayment

Felt or recycled fiber underlayment shows up a lot under engineered wood and sometimes under click floors. It is thicker and heavier than basic foam.

These are often made from:

• Recycled fibers
• Textile blends
• Cellulose‑based fibers

Pros:

• Good support under wood
• Better sound dampening than thin foams
• Can feel more solid underfoot

Cons:

• Moisture handling varies a lot by product
• Some require a separate vapor barrier over concrete
• Not all are designed for vinyl or very thin floors

Best for:

• Engineered wood floors, both nail‑down and floating, where the manufacturer recommends it.
• Projects where you want better feel and sound than a cheap foam, but not full rubber pricing.

Combo and specialty underlayments

Then there are multi‑layer products that try to do everything in one:

• Foam or rubber core
• Attached vapor barrier film
• Sometimes a built‑in tape edge or lip

These usually market:

• Sound control
• Moisture barrier
• Thermal insulation

They make sense when:

• You need to meet a specific IIC/STC target.
• You are over concrete and want a single step solution.
• You are installing laminate or vinyl in a condo and need documentation.

When builders need to show a board or HOA that the floor meets sound rules, they almost always pick a tested combo underlayment and keep the spec sheet on file.

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Matching underlayment to your floor type

Now let us get practical. The right underlayment is different for laminate, vinyl, engineered wood, solid wood, and tile.

1. Laminate flooring

Laminate is almost always a floating floor, which makes underlayment critical.

Key questions:

• Is the laminate pre‑attached with pad?
• What does the laminate manufacturer recommend or forbid?
• Is your subfloor concrete or wood?

a) Laminate with no attached pad

• Over concrete: foam with vapor barrier, rubber with barrier, or combo underlayment tested for laminate.
• Over wood: foam, cork, fiber, or rubber, depending on sound needs.

b) Laminate with attached pad (pre‑padded)

Here people often make a mistake. They add another full underlayment layer on top of the attached pad.

Problems:

• Floor becomes too soft.
• Click joints carry extra stress and can fail.
• Warranty can get voided.

If your laminate has attached pad:

• Over concrete: usually only a thin vapor barrier is allowed, not thick underlayment.
• Over wood: often no extra underlayment is needed, unless the manufacturer lists a compatible one.

Always check the manual. Many brands say: “Do not install additional underlayment under pre‑padded product.”

2. Luxury vinyl plank (LVP) and tile (LVT)

Vinyl is tricky because it is thin and sensitive to movement and texture beneath.

There are two big groups:

• Click‑lock floating vinyl
• Glue‑down vinyl

For sound and moisture, we are mostly talking about click‑lock.

Questions:

• Does the vinyl have built‑in pad?
• Is the product SPC (rigid core) or WPC (wood‑plastic core)?
• Does the warranty allow any underlayment, and if so, which types?

a) Vinyl with attached pad

Very common now. Often the manufacturer:

• Does not want another cushioned underlayment under it.
• Only allows a thin vapor barrier film over concrete.

Check for specific language like:

• “Additional foam underlayment is not approved.”
• “Use only 6 mil poly over slabs.”

b) Vinyl without attached pad

Here you have more options, but you still can not just pick anything. Vinyl does not like:

• Very soft, spongy underlayments
• Underlayments that hold moisture against its backing

Safer choices often include:

• Thin, high‑density foam rated for vinyl
• Rubber or combo underlayment where the product sheet mentions vinyl/LVP

Over concrete, you usually want a vapor barrier as part of the system.

For multi‑family vinyl installs:

• Look for underlayment with clear test data for LVP/LVT over concrete or wood.
• Check that the flooring brand approves that level of cushion.

Vinyl tolerances are tight. More cushion does not always mean more comfort. It can mean shorter floor life.

3. Engineered wood flooring

Engineered wood can be:

• Floating click
• Glue‑down
• Nail‑down or staple‑down

Underlayment rules change with each.

a) Floating engineered wood

Very similar to laminate in behavior, but usually more sensitive to moisture.

Typical underlayments:

• Cork
• Rubber
• High‑density foam
• Felt / fiber mats

Over concrete:

• You need a vapor barrier, either separate or integrated.
• Some wood brands have specific systems and do not want generic barrier that traps moisture improperly.

Over wood subfloors:

• Often more forgiving.
• You can pick cork, felt, or rubber based on sound needs.

b) Glue‑down engineered wood

Here underlayment is different. There are two main methods:

• Glue directly to the slab or subfloor with an adhesive that includes moisture control.
• Glue to a sound control mat that is bonded to the subfloor (acoustic mats designed for glue‑down).

Standard floating underlayments usually do not apply here. You need sound mats and adhesives designed for glue‑down systems.

c) Nail‑down / staple‑down engineered wood

Underlayment is usually more like a paper or felt layer:

• Builder’s felt or specialized wood floor underlayment
• Sometimes a sound control pad under plywood in advanced systems

Sound control is often handled with:

• Special joist insulation
• Resilient channels
• Ceiling assemblies below

So the underlayment alone is not doing all the sound work.

4. Solid hardwood

Solid wood does not like moisture. At all. So:

• Over concrete: usually not recommended without special systems.
• Over wood subfloor: traditional method uses a rosin paper or felt underlayment.

Sound control with solid wood usually happens outside of the underlayment layer. Builders focus more on:

• Subfloor stiffness
• Ceiling assembly

If you need strong sound performance with a wood look and you are over concrete or in a condo, engineered wood or LVP with proper underlayment usually works better than solid hardwood.

5. Tile and stone

Tile underlayment is its own subject, but for sound and moisture:

• Acoustic mats exist that go under thinset and tile to control impact noise.
• Some are rubber or cork based, some are specialized membranes.

Over concrete:

• You may still need moisture control below the mat.

Over wood:

• You usually have backer board or membranes plus acoustic mat in sound‑sensitive builds.

If your main goal is sound, and you want tile in a condo, you almost always need a tested, rated acoustic membrane under it.

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Matching underlayment to your subfloor

Now let us lock in the other half of the picture: what you are installing over.

Concrete slab (or basement floor)

Concrete and moisture are close friends. Even if the floor looks dry, vapor can move through the slab.

Questions:

• Is the slab on grade or over living space?
• Is this a basement?
• Have you done a moisture test?

For floating floors over concrete, the default safer path:

• Use an underlayment with a vapor barrier, or
• Use a 6 mil poly sheet plus an underlayment approved over that.

Good fits:

• Foam with attached barrier (laminate).
• Rubber underlayment with barrier (condos with sound rules).
• Combo underlayment rated for your exact floor type.

Over concrete, cork or plain felt by themselves are risky because they can absorb moisture. If used, they usually sit on top of a separate vapor barrier sheet.

Wood subfloor (plywood or OSB)

Wood subfloors move with humidity but do not push moisture upwards the way concrete does.

So:

• Vapor barrier is less about the slab and more about the room conditions.
• You often do not need a full barrier sheet for floating floors.

Here, you can usually focus on:

• Sound performance (foam, cork, rubber, felt).
• Support and feel.

If the space below is humid (like an unfinished crawlspace), then you tackle moisture at the crawlspace level:

• Ground vapor barrier
• Ventilation or conditioning

Then choose an underlayment that your floor manufacturer likes over wood.

Over existing flooring

Some people float new floors over old tile, vinyl, or wood. That can be fine, but you need to think through:

• Height buildup (extra layers add up).
• Moisture trapped between layers.
• Manufacturer approval (they sometimes forbid this).

If allowed, underlayment choice usually treats the existing flooring like the subfloor material:

• Tile or vinyl over slab: underlayment with barrier.
• Old hardwood over wood: pick underlayment for wood subfloor.

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How to choose based on your building type

Your building matters almost as much as the floor.

Single‑family homes

In a detached house:

• Sound control is more of a comfort choice than a legal one.
• Moisture is the bigger long‑term risk, especially over slabs and basements.

Common choices:

• Laminate over wood: basic or premium foam.
• Laminate over slab: foam with barrier or combo pad.
• LVP over slab: thin foam rated for vinyl plus barrier, or product‑specific underlayment.

If you are above a finished basement and you want less foot noise below, stepping up to a better foam or rubber pad can help, but do not expect miracles without ceiling upgrades.

Condos and apartments

Here you need to slow down and check documents:

• HOA rules or condo bylaws for minimum STC/IIC.
• Any approved product lists.
• Floor manufacturer requirements for multi‑family.

You will often need:

• An underlayment with published test results over 6″ concrete.
• Documentation you can send to management or the board.

Practically, in condos:

• Rubber or high‑performance combo underlayments are common.
• Basic foam is rarely enough to meet their numbers.

Before you buy anything, ask your building: “What IIC and STC do you require for hard surface flooring, and do you have any approved underlayment systems?”

That one email can save you from ripping out a brand new floor later.

Light commercial spaces

In offices, studios, or retail:

• Noise can be a comfort problem and sometimes a lease issue.
• Floors see more traffic, so underlayment must hold up.

Rubber and dense fiber products usually work better long term than cheap foams here.

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Common underlayment mistakes that cause sound and moisture problems

You probably want to avoid learning these lessons the hard way.

• Doubling up underlayments: Putting foam over attached pad, or foam over foam, to “improve sound.” This often breaks floor joints and voids warranties.
• No vapor barrier over concrete: Installing a floating floor on concrete with only a basic foam, then seeing cupping and warping later.
• Wrong underlayment for vinyl: Using squishy laminate foam under thin LVP, leading to movement, gaps, and lock failure.
• Ignoring manufacturer instructions: Floor brands are strict about underlayments. Ignoring their conditions is risky.
• Relying on underlayment to fix bad subfloor: Big dips or humps need real leveling. Underlayment is not a magic patch.
• Not sealing vapor barrier seams: Leaving gaps, tears, or holes in barrier film and assuming it still works.

One layer of the right product beats two layers of the wrong one every time, both for sound and floor life.

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A step‑by‑step way to pick the right underlayment

Let me give you a simple process you can follow. This helps you cut through marketing and match what you actually need.

Step 1: Identify your floor type and brand

Write this down:

• Laminate, LVP/LVT, engineered wood, solid wood, or tile.
• Product name, brand, and whether it has attached pad.

Then read:

• The installation guide for that product.

Look for words like:

• “Approved underlayments”
• “Do not install over foam underlayment”
• “Vapor barrier requirements over concrete”

If the guide is vague, check the manufacturer’s website or call support.

Step 2: Confirm your subfloor and location

Write down:

• Concrete slab, wood subfloor, or something else.
• Which floor of the building you are on (basement, ground, upper story).
• Space below (another unit, garage, basement, crawlspace).

If you are over concrete:

• Plan for moisture control in the design unless you have proper testing and a system that addresses it.

Step 3: Check building or HOA sound rules

If you are in a multi‑family building:

• Ask for written STC and IIC requirements.
• Ask whether they require test reports for your system.
• See if they have any listed products already approved.

If nothing is specified:

• Aim for underlayments that, with your floor type, show IIC and STC close to or above 50 over 6″ concrete in their test data.

Step 4: Shortlist underlayments that match all three

Now cross‑filter:

• Remove anything your floor brand forbids.
• Remove anything that is clearly not suited for your subfloor (no barrier over slab if a barrier is needed).
• Focus on products where the datasheet mentions your floor type.

From what is left, compare:

• Sound ratings (if given)
• Thickness and density
• Moisture properties

Step 5: Make your tradeoffs

Now you balance:

• If sound is critical: lean toward rubber or high‑performance combo pads with strong IIC numbers.
• If moisture is the main worry: lean toward integrated vapor barrier systems approved by your floor manufacturer.
• If cost is tight: high‑density foam with barrier (for laminate), or a simple barrier film plus approved pad.

If you get stuck between 2 or 3 products, ask the underlayment maker:

• “Do you have a test report for this product under [my floor] over [my subfloor]?”

The better brands usually do.

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Real‑world example setups

Let me walk you through a few typical scenarios so you can pattern‑match yours.

Scenario 1: Laminate in a condo over concrete

Details:

• 6″ concrete slab between units.
• HOA requires STC 50 / IIC 50.
• Laminate with no attached pad.

Good path:

• Pick a tested rubber or combo underlayment with IIC 70+ and STC 60+ reported over 6″ concrete and laminate.
• Make sure it includes or works with a vapor barrier.
• Send product data sheets to the HOA before buying.

Avoid:

• Generic 2 mm foam from a big box store with no acoustical data.

Scenario 2: LVP over basement slab in a house

Details:

• Concrete basement floor.
• Click‑lock SPC LVP with attached pad.
• You care more about moisture and mold than neighbor noise.

Good path:

• Follow flooring manual: usually install a 6 mil poly vapor barrier directly on the slab.
• Float the LVP with attached pad on top, no extra foam.

Avoid:

• Adding extra foam with barrier under the attached pad “for comfort.”

That can cause too much flex and risk the joints.

Scenario 3: Engineered wood over wood subfloor in a second‑floor bedroom

Details:

• 2×10 joists with plywood subfloor.
• Floating engineered wood with click joints.
• You want less noise to the room below, but there is no HOA.

Good path:

• Choose a cork, felt, or rubber underlayment approved for floating engineered wood.
• Aim for products with better IIC ratings tested over wood frame systems if possible.

You do not need a full vapor barrier here unless the manufacturer says so.

Scenario 4: Office space with LVP over old concrete

Details:

• Old slab, some minor uneven spots.
• Click LVP without pad.
• Sound is a comfort issue in open offices.

Good path:

• Level the worst dips with patch or self‑leveling compound.
• Install a high‑density underlayment rated for LVP with integrated moisture barrier and acoustic benefit.

Rubber or premium combo underlayment can make a big difference in walking sound and feel.

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How to double‑check you are not breaking the warranty

Manufacturers are quite strict, especially higher quality floors.

Simple checklist:

• Download the installation guide for your exact floor.
• Search for “underlayment,” “pad,” “vapor,” “concrete,” and “sound.”
• Write down any phrases like:
  • “Do not use X”
  • “Must use minimum 6 mil poly over slab”
  • “Use only underlayments with compression strength between X and Y”
• Email the manufacturer with the underlayment name and ask: “Is this approved under your warranty for [my subfloor]?”.

Most support teams will respond, and that email is something you can save in case there is a problem later.

If a product page says “universal underlayment for any floor,” be skeptical until the flooring brand also agrees with that claim.

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Practical tip to finish: test a small area before going all in

Before you commit an entire floor:

• Install a small section: 4-6 rows over your chosen underlayment.
• Walk on it with different shoes.
• Listen for hollow sound or too much bounce.
• If you can, have someone walk while you listen from the room below.

If it feels off, now is the time to adjust underlayment choice or add structural sound treatments, not after the whole floor is in.