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.
These are the best non-toxic low-VOC options with a focus on the material composition.
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Paper Underlayments Used Under Wood Floors
Silicone Paper
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
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.
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 vapour barrier.
Best practices, 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
Breathable Cork
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, and hardwood flooring.
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.
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.
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.
My flooring post goes more into detail on brands of non-toxic floors.
Underlayment for Tile
I like the Schluter system under tile.
They have 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.
Underlayment for Carpet
The main healthy options are natural wool felt for wool carpet, polyethylene, synthetic rubber, or built-in synthetic felt.
My carpet post goes into detail on underlayment for carpet.
Corinne Segura is a Building Biologist Practitioner with 6 years of experience helping others create healthy homes.
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Rachael Bonsignore says
Hi Corrine. Have you found out anything about the possible toxicity of Iron Ply that is used under linoleum in the bathroom? It looks like a kind of thin plywood. It looks benign, but I started getting symptoms after it was installed- very loud ear ringing, chest or lung pain…Could be the wood itself I am reacting to, or something else in the house (a little bit of spray foam used recently or vinyl siding stored in house). I didn’t smell anything when I put a piece of it up to my nose, but I did smell a strong chemical smell on it after I soaked it in water for an hour or so.
Corinne says
I haven’t seen that before, could you ask them what is in it?
Anne Robinson says
Hi there-
Thanks so much for all this information.
We are using self-leveling concrete on our basement floor and then buying wool carpet with wool padding. Are there any concerns with self-leveling concrete?
I have looked all over the internet but have not found definitive information. The self leveling was our only option as redoing the floors entirely was beyond our budget and would have lowered the wall height. Should we air out for a long time after using the self-leveling concrete?
Corinne says
Most of them are 0 VOC.
zuzana says
Hi,
I bought recycled hardwood floor which I would like to lay in my basement apartment. What underlay would you recommend for the basement flat? I am confused about the vapour barier! The floor is concrete.
Many thanks,
Zuzana
Corinne says
I personally would not put any type of wood over a concrete basement floor or slab on grade due to moisture. People do this, it’s the norm but mold is also the norm in buildings.
Poon says
Thank you so much Corrine for all the information. Would you suggest using Quietwalk plus under solid unfinished hardwood floors? Thanks.
Corinne says
I would talk to your installer about that, since it’s mainly specified for floating floors.
Hawnes says
Hi Corinne, thanks for the informative post.
I want to install linoleum upstairs. What would you recommend for either linoleum sheet vs. click as an underlayment?
Thanks.
Linda says
Corinne,
Thank you for sharing this valuable healthy living information. You mentioned not to install flooring that requires a vapor barrier over a slab. I am having a concrete slab house built and am trying to be as green and non-toxic as possible. Mold terrifies me.
What type of floor that does not require a vapor barrier can be installed over a concrete slab? Also, is it possible to put a raised sub-floor to eliminate the need for a vapor barrier, if I can get the builder to do it?
Thank you,
Linda
Charlotte, NC
Corinne says
Hi, polished concrete or tile or yes like you mention a “sleeper system” which is raised up. I would have Cheryl Ciecko detail that.
Linda says
Thanks.
Tatum says
Corinne,
Can you clarify doing polished concrete if you are under grade as I thought I read you recommend against sealing the slab (epoxy or other) due to ensuring it dried to the inside?
Wouldn’t polishing it prevent it from drying to the inside?
I appreciate the clarification as I’m trying to figure out our best flooring route for our finished walk-out basement. The north wall is completely under grade, while the west and east are partially under grade and the south wall is fully walk-out.
Blessings,
Tatum
Corinne says
Polishing with (sodium/potassium/lithium) silicates is breathable according to the building science experts I work with.
Jonathan says
Thank you so much Corinne, this is very helpful!
I called MP Global regarding Quietwalk and they said the use Polyphase 678 antimicrobial made by Troy (http://www.troycorp.com/product_view_Preservatives.asp?unitName=Preservatives&cat=products&sub=functions&ID=483) in their Quietwalk underlayment. The product info sheet (which I found doing a search since Troy requires an account) seems concerning. What are your thoughts?
Would something like FloorMuffler be a safer choice? https://www.floormuffler.com/products/floormuffler/
Thanks so much!
Corinne says
Green Building Supply sells quietwalk without the antimicrobial.
Jonathan says
Ahh yes, I forgot you mentioned that! Thanks!