There are a variety of underlayments used under wood floors, click-together floating floors, as well as carpet and tile.
Underlay can serve various functions like cushioning, sound deadening, leveling, uncoupling, and moisture resistance.
The following underlayments are relatively high in offgassing (too high for me):
- Polyurethane foam
- Most cork underlayments, except the ones listed here
This post goes over the best non-toxic low-VOC options.
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Paper Underlayments Used Under Wood Floors
Silicone paper is usually used under real solid hardwood floors, but it can also be used under engineered wood. It is semi-permeable which is good, as you want your upper floors (over wood subfloors) to be breathable in almost all situations.
It meets perm ratings recommended by the National Wood Flooring Association.
Those extremely sensitive to chemicals have liked this product a lot. If you just need something simple that is not providing sound dampening or leveling this will do the job.
Red Rosin Paper
Tried a true, Red Rosin is the old school underlayment paper used under real wood flooring. It’s extremely low in odor and even that dissipates rather quickly. The extremely sensitive almost always do well with this, with only a few people mentioning that the undyed Rosin Paper was preferred.
This is what I would use under wood floors. Keep it simple and breathable.
Foam Underlayments for Click Together Floors
Basic Polyethylene Foam
For laminate, engineered and other click-together floating floors I prefer the most basic polyethylene underlayment. It’s very simple – it’s one of the safest plastics in terms of odors and offgassing (it’s zero-VOC).
This provides some cushioning which is necessary under flooring types like laminate.
It’s not a complete vapor barrier, so it can breathe, which is great for upper-level floors. Plus, it’s very inexpensive.
This is the type of foam that comes pre-attached in some laminate lines. I find that very convenient.
A “2 in 1” will usually have polyethylene foam and a thin layer of plastic. If you are looking for a vapor barrier, make sure it has one attached. The term 2 in 1 is rather confusing in this sense, as some are moisture-resistant and some have vapor barriers, but they are very thin.
Check with the flooring company and your contractor to make sure you have an appropriate vapor barrier, if one is required.
Cali Bamboo brand makes a good polyethylene underlay with foil as the vapor barrier, made for their floating floors. And Kahrs makes a polyethylene foam with 3 mil poly plastic for their engineered floors.
Some are just the foam, which is the type I would use over wood subfloors.
Polypropylene foam is another very safe plastic. It’s not as breathable as polyethylene and I have only seen it advertised as being a vapor barrier or as having a vapor barrier (another plastic layer) attached to it.
It’s used for laminate and engineered (mostly) when a vapor barrier is required. It can be used under solid hardwood floors to provide cushioning and sound dampening.
If it’s labeled 3 in 1 that usually means it’s cushioning, sound dampening, and a vapor barrier.
Floor Muffler has not tested their products with carpet. Their polypropylene underlayment is free of any added flame retardants.
They have a high acoustical rating, the one below can meet IIC up to (74) dB per ASTM E 492 / ASTM E 989, STC up to (73) dB per ASTM E 90. Mohawk Silent Guard is STC 73, IIC 71.
EVA foam is another safe foam. Compared to polypropylene and polyethylene it does have slightly more of an odor.
EVA foam underlayment can be used under floating floors like engineered wood, laminate, bamboo, and vinyl as well as carpet.
IIC (Impact Sound Transmission Test) rating is 73, STC (Sound Transmission Class) is 72.
Felt Underlayment For Engineered Floors
Felt + Vapour Barrier
Quietwalk is felt and a vapor barrier made for under laminate and engineered wood as well as other floating floors like bamboo and luxury vinyl plank.
The felt and (polyethylene) plastic layers are quite safe even for the chemically sensitive. It claims to be zero-VOC.
This one does contain Microban (Microban can refer to hundreds of chemicals, so this could be anything from silver to something more synthetic). If you want it without antimicrobials you can get Quietwalk from Green Building Supply.
Because this has a vapor barrier it’s meant for on top of a slab or basement floor. If you do lay down laminate, engineered, or another organic-based click-together floor on a slab or basement you do need a vapor barrier.
Best practice, according to mold preventative architects, is not to apply flooring that requires a vapor barrier over a slab because a concrete floor is always trying to dry to the inside. As a mold-sensitive person, I can smell the mold that festers underneath when a vapor barrier is applied. And it happens in most homes in my experience.
Natural Material Underlayment For Many Floor Types
Cork underlayment is one of the most expensive underlayments. It provides good cushioning and sound dampening as well as some leveling.
It can be used under engineered hardwood, laminate floors, hardwood flooring, and ceramic tiles.
The small pieces of cork are usually pressed together with a polyurethane glue which I find to be quite strong in offgassing, so I don’t personally use this underlayment. However some brands are made with polyethylene as the binder, which is much much better in terms of odor and offgassing. Eco Cork Foam, says they use polyethylene as the main binder.
They also recommended to glue the underlayment down.
There are many flooring types and brands that come with an already attached cork underlayment, which also always has this polyurethane offgassing odor.
1/2”(12mm) cork underlayment has STC 49 and IIC 48 sound ratings.
Cork with a Vapour Barrier
Eco Cork Foam is not as natural as the pure cork above. This version combines cork with polyethylene foam and a 6 mil poly vapor barrier.
Pressed Wood Underlayment
This Steico product is a lot more unusual than the others. This is different from the old particle board underlayments. They claim it is more water-resistant than particleboard.
It’s a pressed wood product, but they don’t mention what kind of wax, oil, or glue is used to make it. They do claim it is zero-VOC.
It can be used under floating floors like LVT, laminate, and engineered wood, as well as hardwood floors.
It seems to be very good at sound dampening.
Vapor Barrier for Over a Slab or Basement Floor
6 Mil Poly
This is the most common vapor barrier for slabs and basements. If I was going to put down a vapor barrier (which I wouldn’t due to the reasons discussed above) I would go with plain 6 mil polyethylene plastic. There is no need for anything fancy here. Though it does not provide cushioning. If cushioning is required it makes sense to buy a foam and vapor barrier in one. I would make sure it’s 6 mil though.
Flooring with Attached Underlayment
Many click-together floors come with an attached underlayment. This really helps in simplifying things.
I like laminate floors with polyethylene foam backing attached, LVP with rubber underlayment attached, and engineered flooring with cork already attached.
Luxury Vinyl Plank (LVP) with a cork backing does not make sense to me in a basement, slab or wet area since one of the main benefits to LVP is that it is waterproof and very mold resistant.
Some LVP comes with a EVA underlayment.
Underlayment for Tile
I like the Schluter system under tile.
If you need zero-VOC acoustical control under tile Schluter DITRA-HEAT-DUO providers a ΔIIC contribution of 20. Cork underlayment can also be used under tile.
Schulter has different membranes that I discuss more in the grout and thinset post. They are made of a non-toxic very low odor plastic that even chemically sensitive folks do well with.
Many acoustical underlayments for tiles are rubber-based, and I would personally avoid those as they are one of the highest offgassing products in a home. (Whisper mat is one that is mostly foam with some asphalt adhesive, so that would be an improvement over most rubber underlays).
Laticrete Fracture Ban is not toxin-free but it’s one I have seen that the company says is breathable. LL Floors Fiber Fusion Anti-Fracture Crack Isolation Membrane is also breathable according to the company.
Photo Schulter membrane from Amazon.
Underlayment for Carpet
My carpet post goes into detail on underlayment for carpet.
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.