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Bubble wrap: sauna building secret #5

Building a sauna without using foil bubble wrap is like building a shower and tiling right on sheet rock.  It may work for awhile, but at some point it may very well get yucky.  When you are offered such a wonderful product, it’d be a shame not to use it.

Foil bubble wrap

  • is easy to apply: just use a staple gun and staple it to your studs.
  • is easy to work with: foil tape your seems and around light switches, etc.
  • performs fantastically: heat gets radiated back into your sauna and it creates a superior vapor barrier, protecting your structure and isolating moisture and loyly.

Foil bubble wrap is finding applications well beyond sauna.  It is an emerging building material that you’ll be seeing more of, in more practical applications and uses.  Foil bubble wrap automobile?

Home building centers sell foil bubble wrap in the insulation department.  Here’s Ace Hardware’s offer.

 

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40 thoughts on “Bubble wrap: sauna building secret #5”

  1. Hi Iam building a sauna. Was wondering about the bubblewrap it says its not rated for over 180 degrees. I know that is hot but couldn’t parts of the sauna get that hot. I will take some pictures. I probably put it on the bottom parts where it is cement block. Thanks chris

  2. Where did you find the spec information regarding 180 degrees Chris? I am looking for materials to construct an insulated version of a barrel-type sauna and was thinking about this product.

  3. Yes. Foil bubble wrap is the best, my opinion. And it is readily available. Some use straight reflective foil wrap, without the bubble behind, and this is great product too. I like the Depot / Menards big box availability and ease of use with the foil bubble product. Just me.

  4. Can anyone comment about the use of foil-backed insulation (as a vapor barrier and additional insulation) between the studs and the interior cedar T&G for a sauna. It would replace the foil vapor barrier.

  5. Eric: You can use this yet I prefer the foil vapor barrier as it creates a complete vapor envelope of entire hot room. Foil backed rigid is good, but you have exposed wood studs, and potential minor air breach between joists (studs). Best to cover everything with foil reflective vapor barrier when conventional frame building our saunas.

  6. Yes, we foil wrap over insulation. Unwrapped insulation is best. And be sure to foil tape the seams and around fixtures, etc.

  7. Hi Glen, I’m using an aluminum coated paper available here in Canada which is a fraction of the cost (10c/sqft). No plastic content which is great.
    I’m an engineer with a background in thermodynamics so I did my homework on the bubble wrap and couldn’t find any tangible benefit to justify the cost.
    We’re using lots of your ideas from the book and hoping to have our sauna complete for Christmas so thanks!

  8. Camm: Thanks for the input. Aluminum vapor barrier is a great thing. (reflective and moisture barrier). We tend to go with foil bubble wrap as it is readily available at big box Depots/Lowes/Menards here in USA. Your no plastic content is a bonus. Further, your product lays flat, making t&g application that much easier. (it’s a bad move to overlap foil bubble wrap). Send me a link to the mfr. if you have it. I’m interested.

    More importantly, you being an authentic sauna enthusiast AND an Engineer with a background in thermodynamics, would you like to join our Lampomassa Analysis Committee (LAC)? LAC meets semi annually at the LAKe (my cabin) and you have to pay your own way, but I make great post sauna food. If interested, I’d look forward to reviewing your LAC application, which is a 50-100 word essay on your thoughts and comments regarding:

    https://www.saunatimes.com/sauna-culture/sauna-philosophy/could-lampomassa-become-the-second-finnish-word-to-be-adopted-into-the-english-language/

  9. Does it need to be bubble aluminium? Or will just aluminium wrap work? Also, I have tyvek, the outside plywood is up already, while I wasn’t looking! So should I put the tyvek on the inside now before insulation? Can it go over the 2×6’s then insulation? Can I use sided insulation? It’s what I have… So I have bare exterior walls showing with the studs from the inside… Should I cover them up with tyvek before insulation? Then Insulation, then foil? Thx Brad

  10. One more idea… Seeing how I did not get the tyvek on before the exterior walls… Should I still put it on there? Can it go over the studs on the inside? (I cannot get the plywood off the outside now to get it on there right…) What about the sided insulation? What would hold up non sided insulation? Wouldn’t it just fall down over time? Can I use sided insulation and then the aluminium wrap? So from inside it would be starting with the exterior siding on already bare plywood on bare studs… Should I put the tyvek on first, then insulation? sided? 2×6 walls… Then last the aluminum wrap then cedar tongue and groove?

  11. I forgot the ceiling… that also got put on without the tyvek… So it’s raw rafters with raw plywood already on it… Shall I put the tyvek up first before insulation? Or maybe the sided insulation with side up against plywood then foil? I need some direction obviously… THank you…

  12. Hi Glenn,

    Thanks for the invite, we’d love to come and visit the LAKe cabin to share ideas over some Löyly and Lämpömassa (I also installed radiant floors in our house) to see how its really done! I’ll get onto the essay and get back to you soon. Our sauna is up and running now, we easily get 100 deg C in our hot room with the temperature outside at 20 below. We’re yet to put the finishing touches and complete sealing it, but our lives are already better with our little oasis!

    The product that I used on the walls under the cedar is Scutan (https://www.atlanticcoatedpapers.com/products/vapor/) it comes in rolls that are 50 inches wide and very easy to work with, especially if you have two people. In Canada, I got it at Home Hardware, not sure if the other box stores carry it. If the corners are too tight when you come to installing the cedar, you can easily cut the paper and tape to relieve the tension as you go.

    For Brad above, the Tyvek goes on the outside of the building under the siding, it allows the wall cavities to breathe and prevents moisture from the outside getting in. You don’t need Tyvek ceiling, however, you should have some form of

    On our sauna we have the following layers from outside in:

    Lap siding (pine), Tyvek, Aspenite (chipboard), 1 inch foiled solid foam insulation, Aspenite, 2×4 stud walls with pink insulation, Aluminum paper vapor barrier (Scutan), Cedar tongue and groove.

    The aspenite and solid foam provides additional insulation and a continuous vapor seal which may be a little over the top!

  13. not to my knowledge, no, yet if you hear of something or have a VOC meter and want to test, please reach out!

  14. Hello there!

    I am currently building a sauna just outside Ottawa, Ontario, Canada. We have 80 C seasonal temperature differences between winter and summer. I am building a 6×8 woodstove sauna using concrete “deck blocks” and 2×6 subfloor joist framing with a 1″ treated plywood subfloor sheathing. Given that the subfloor is raised off the ground using concrete deckblocks, how should I insulate/vapor barrier/air barrier the subfloor under the sheathing? I will use Alu foil on the inside of the walls of the sauna UNDER my tongue and groove cladding but how should I vapor barrier the floor under my plywood subfloor? Should I place Alufoil directly under my subfloor, then insulate, then tyvek facing the “cold side”? Any information on how floors should be properly insulated and CORRECTLY vapor tight/breathable if need be would be greatly appreciated!

    Looking forward to my first sweat.

    Cheers!

    Samuel

  15. Samuel:

    Your on the right track. I would use 2” rigid between floor joist cavities flush up to subfloor before laying your subfloor.

    And to prep your floor, this is where I will up sell you and encourage you to click the button on the upper right part of this website and invest in my ebook. In there, you’ll get a detailed explanation of how to do this right. And as a bonus, you’ll get details on many/all other nuances, a few of which I think will really help you along.

    And as an extra teaser, please search “vinyl cement” in the search bar above and you’ll get a super amateur video documentation of another nugget of empiricism.

    Happy for your build and hope this helps!

  16. Hi,

    Great to see this community here!

    My concern about this bubble foil as a vapour barrier is that it might off-gas in these high temps.

    Your thoughts?

  17. Mike:

    If this is a concern, you can use regular foil vapor barrier. A bit harder to find, yet find-able.

    I’ve spoken with trade industry professionals about this product. It is rated for temps well North of 200f. This is good as the temp. behind our wood paneling is less, and the temp behind the foil layer even more less.

    But swallowing all this may be like talking to the Marlboro salesman about healthy living, so, again, if it’s of concern, go with the non poly, poly bi product foil.

  18. for reasons glenn listed, the actual temp where the bubble wrap is located within the wall assembly is much lower than the hot room itself so practically shouldn’t be a concern unless you are blasting the sauna at 225 degrees or something like that. the cost difference between the bubble wrap and ‘traditional’ foil wrap is basically the same, i went with that product for peace of mind. the bubble wrap is definitely more forgiving than the foil wrap though, foil is pretty easy to tear, just need to take your time.

    and unlikely most stores will carry the foil wrap, other than specialized construction stores or sauna supply shops. i ordered mine online, lots of choices out there from reputable sauna suppliers.

  19. many use poly as a vapor barrier for changing room. The key is a moisture barrier keeping it away from the joist cavities.

    Re: lämpömassa and heaters, we want to keep in mind that amount of rock is not equal to lämpömassa. Some rock is mainly cosmetic and doesn’t get hot. But you’re rocking, and that’s a good thing.

  20. stephen, if an outdoor unit, you will want to provide a vapor barrier on the exterior walls of the changing room, like any other type of occupied structure construction. foil barrier would work but is expensive/tedious compared to good ol’ faced fiberglass batt insulation. place in stud cavity, staple paper ‘tabs’ to face of stud, done.

    but what about the interior shared wall between the hot and changing rooms? does that wall require any vapor barrier on the changing room side? my advice is NO. foil barrier (the paper or bubble stuff) has a very low permeability, meaning moisture does not pass through it easily. so by placing a barrier on the changing room side of the shared wall, you have now created a ‘vapor barrier sandwich’. any moisture that finds its way into the wall will have a very hard time getting out (and believe me, moisture always finds a way into the wall cavity). damp walls can lead to mold growth and other bad stuff.

    and technically all these products are called vapor ‘retarders’, not barriers. they all allow some moisture to pass through, some just much more/less than others. so on the exterior walls, the house wrap on the exterior side is a vapor retarder but more permeable than faced insulation (typically five times more permeable) and much more permeable than foil insulation (like, 50+ times more permeable). moisture in exterior walls is not as great a concern as it can ‘vent’ to the exterior through the house wrap.

  21. Hi thanks for all the great information! I am currently in the middle of turning a basement pantry into a sauna. I have a couple questions. First to I need to leave a gab between the foil bubble wrap and the cedar? Also the room has foundation wall (concrete) in it. Does that wall need to be covered and insulated or can it remain expose?

  22. Daniel:

    you’re welcome!

    Gap between foil vapor barrier and cedar is not critical. Some apply firing strips and allow for an air gap between cedar and the foil (thermal bridge).
    Concrete wall: for sure, you very much should isolate this from your hot room. Otherwise, you’ll be struggling to heat up the room, because that foundation slab will suck all the heat out of the room. I’d apply rigid foam between 2×2’s and then foil, then cedar.

    Hope this sets you in the right direction!

  23. Hi, I’ve read a lot of conflicting information about whether or not Tyvek is necessary for the exterior of an outdoor sauna. Will moisture get into the structure if I skip it?
    Thanks, Angela

  24. My vote/bent is to Tyvek the outside of a sauna building. The concern of moisture within joist cavities only becomes real if we don’t build our saunas the right way, which includes foil vapor barrier in our hot rooms, well sealed seams. Tyvec is a breathable compound.

  25. Building a Turkish Hammam as traditional as I remember. However, our builders don’t know anything about it.
    They have put concrete board up, and plan to build it like a shower.
    Seems like we should put insulation (the same as you use in a home) and then put the foil bubble wrap and tape and THEN this concrete board? The plan is to get the radiant floor heating working that is under conrete and foam slab… THANK YOU

  26. Rose:

    I hear you. Builders know nothing about Turkish Hammam. If I were to build one, i’d be thinking about rigid or spray foam vs. any kind of batting. And i’d be thinking metal studs as well.

    If I were building a Hammam, i’d be building it with the idea that if the entire structure was sunk underwater for extended time, then brought back to the surface, it would continue to be happy (ie no mold or moisture trapping and all moisture capable materials).

  27. I am building a 7’X9′ sauna in a new construction project at our home in Brighton UT. 3 Exterior walls and 1 interior wall are 2×6 framed with 2″ spray foam and 3.5″ unfaced fiberglass insulation. Building codes require extremely beefy framing due to snow load. This means double/triple stud packages everywhere and solid headers over the windows. My concern is about losing heat through all the solid framing.

    Is it uncommon to sheet the interior walls and ceiling with foil faced poly-iso insulation (foil facing hot room) over all the framing and foil taping the seams to create a complete thermal break from framing to hot room. This would also double as a vapor barrier would it not?

    Thanks for all the good info!

  28. Scott:

    Your question: so good and so timely! Short answer is “yes, poly-iso will create a complete thermal break.” Now, if you bring this forward to social media discussion boards, you’ll be sure to get a lot of cryptic “no’s” with scary push backs like “off gassing” and “flammable.”

    I have been in discussions with Johns Manville (makers of polyiso) as well as PIMA (Polyiso Insulation Manufacturing Association) with intent to get to the bottom of this.

    And the bottom line is poly-iso is is rated up to 250°f. Their tests state that off gassing only occurs at point of manufacturer, and within 20 days after manufacture, until all the elements are fully cured, regardless of service temp. up to rating of 250°f.

    So, your inquiry is just ahead of a comprehensive article on this subject, soon to be published on this website. But you are thinking in a parallel universe here.

  29. Wonderful forum. Thanks for the great information.

    I’m building an 8×6 sauna in the basement of my home. Heater is a Finnleo Designer Pure SL2 and I am aiming for T+G Clear Cedar to arrive this week. Framing is done for a height of 7’3″ to keep my feet close to the the height of the rocks. I’m in a good place, but have a few questions.

    1. The floor is concrete. Necessary to insulate? If so, should I lay down a rubber membrane?
    1a. My plan was to keep the concrete floor, build a 3-4in duckboard, and vent below heater and on a side wall.
    1b. Should I duckboard around the edge of the heater and allow standard 6″ space beneath the unit? Or just duckboard beneath too and allow for ~3″?

    2. I purchased 6mm plastic sheeting and Reflectix aluminum bubble wrap for my vapor barrier. Can I lose the plastic sheeting? Is it better to use aluminum foil barrier AND aluminum bubble wrap? Or is the bubble wrap enough?
    2a. I’ve purchased r-15 insulation, which has a paper wrapping. That’s okay? Don’t think I can find loose insulation and I’ve never used spray.

    3. Due to the layout (I put the door all the way to one side) the lower bench on the 6ft edge of my sauna doesn’t really have room to fit legs bc heater is too close. My plan is to keep the layout because it still gives me a foot rest for the top bench, which I’m prioritizing. I’d upload the layout but not sure how.
    3a. What are best seating depths? I was planning for 20″ up and 18″ lower.

    4. Any aluminum tape will do?

    Thanks for any insights. Love the site and all the information.

  30. Hi Tim:

    Glad you are enjoying saunatimes. Let me try to attack your questions.

    1. insulate floor. There is no absolute answer here. Keep in mind that many cabin saunas have deck flooring open to the world below, so no insulation. These saunas are heated with wood, and wood stoves can beat back cold underneath. But with hot air rising, the floor, generally is not a major problem, unless it’s an ice cold slab in the garage. So how’s that for a vague answer?
    1a 1b. I like your heater sitting on the cement slab and your duck board raised up 6″ (I call this the 3rd bench also). the Finnish police will approve and you’ll be less likely to issue you a citation for violating the “law of löyly” as you’ll be getting that much closer for your feet to the height of the rocks, which is good sauna build design.

    2. Lose the plastic sheeting. Use either aluminum foil barrier or aluminum bubble wrap. I’m a fan of the bubble wrap mainly in that it’s in stock at all big box Depot/Lowes. The service temp for Reflectix is 180°f. which shouldn’t be a problem. It goes like this: hot room: 200°f. Our testing and modeling shows that if hot room is 200°f. Cedar face is about 180°f. and 160°f. on back edge, which is the edge close to your foil bubble wrap. If these numbers don’t make you comfy, then I suggest to go with the higher rated material.

    I’ve used foil bubble wrap for many builds and all are doing just fine. No material breakdown, and I sense some aufgussing when Germans show up but no off gassing (because I don’t smell anything and I’m still alive, but that’s just my take).

    2a. In a perfect world, you’d use unfaced batting. Some get worked up about the black stuff on the paper as not heat sensitive material, and the double vapor barrier that faced insulation creates. Also, on exterior wall, i’d be thinking about pink rigid insulation vs. batting (moisture resistant).

    3. Hot room layout: I’d see about 24″ upper and 14″ lower. You’ll be spending most all your time on the upper bench, and having 24″ will allow you to sit sideways up on the bench, or lay down, without a feeling of falling down.

    4. Aluminum tape: they sell the good stuff right where you can purchase foil bubble wrap. Tape all the seams well.

    Happy to help~!

  31. Amazing. Thanks for the feedback.

    Follow-up:

    1. I don’t think I will insulate the floor. It’s a chilly basement, but I’d rather use that vertical space lost to an insulated flooring to allow for getting my feet above the sauna rocks! Also, if it’s a bother I can always go back and insulate it.

    1ab. Am I allowed to sit the heater directly on the slab? Brochure said 6″ to protect against combustion. Cement won’t blow up, but I was thinking to put a vent underneath.

    2. I’ll stick to bubble wrap. Already purchased.

    2a. No “exterior” wall on the build. However the back of the sauna is close to the foundation wall. Right now I’m t+g/foil bubble/batting/drywall/furring strips/foundation wall … should be okay, right? Guess I could add pink rigid to back side, but would be a tight 3.5″

    3. I’ll do 24″ and maybe 16″ — need to see how much space that would leave me on the floor.

    I’m gapping the door 4″ too!

  32. Hi Glenn,

    We bought a 1965 rambler and have a space in the utility/laundry room to become the sauna (6+ x 7.5ft). We did some renovation with the rest of the basement, gutted to stud walls and spray foamed the exterior walls. The sauna area was not included in the foam except one wall where the contractor sprayed the back side of the exposed existing sheetrock. Would we experience off gassing if we kept the 1/2″ sheet rock (with spray foam on back side in wall cavity), foil or bubble foil wrap and tape, then T&G cedar? It would be the wall our backs would be against, not the stove side (electric). Haven’t framed it out yet and trying to determine if it is necessary to pull off the sheetrock and cut out the foam, or if heat through sheetrock wouldn’t off gas.
    Cheers from the “Lakes Area”, MN!

  33. Mikael:

    With the rise in alternative insulating solutions, it could be said: “for every product advantage, there is an equal and opposite criticism.”

    And a lot of the criticism of spray foam is that it is a relatively new method and it is not free range organic. So, I can sleep at night knowing that spray foam is safely sealed in its upright and locked position behind foil – either bubble or regular. Well sealed and taped. And spray foam has a service temp of . well.. read here for more.

    But I think it’d be important to get that sheetrock out of there. Sheet rock is nadda good anywhere near a sauna.

    It’s kind of like that scene in the Godfather…

    “Leave the foam.. bring the cannolis.”

    cheers to you up in 218!! Hope this helps.

  34. Hi and thanks so much for this site and all your great information! I’m building a sauna on the covered deck off my first level. I’ve already insulated the sub floor with poly foil on both sides of the sub ply and insulating under the decking with solid foam insulation. I’m about to frame the walls – my question is once I insulate the walls and then create the vapor barrier with the poly foil, do you need to leave a small air gap between the foil and the tongue and groove interior walls? I read somewhere that this is necessary (I think it was on a heater manufacturer spec sheet I looked at). If so, I guess I would need to do furring strips on top of the vapor barrier? Your advice is much appreciated in advance. I haven’t had a sauna for several years now and I’m so excited to have one again! Oh, also, I’m building it off of the room’s 8′ sliding glass doors (1 fixed, 1 sliding) and using those as the sauna entry doors. They are not brand new, but not super old either. They’re double insulated glass and have a tight fit all the way around. However, in the winter, they do feel cold. I’m hoping this will work and not lose enough heat to make the sauna not be hot enough to get a good steam. Any advice on this? I can’t find anywhere online where anyone else has done this. I could take them out and frame in a door, but I honestly don’t want to unless I really have to. I could also frame off / block off the stationary door and insulate there, leaving only the 4′ door as access. Worst case I guess if it doesn’t work I can always frame a traditional door in after the fact. I really wanted the glass view into the room it’s off of and I’ve seen a lot of photos of commercial saunas with glass walls. Thanks again! Back to framing for now!
    Amy

  35. Hi Amy:

    Air gap between foil and t&g paneling:
    Major Pandora’s box here, and I’ve gone deep into this topic in Sauna Build Start To Finnish ebook. With an air gap, it is said that the thermal properties of foil are 3x than without.But the thermal properties of foil are pretty close to zero, so go figure there. And with an air gap, they say that the t&g paneling breathes. And for species prone to moisture issues, like aspen, basswood, and the common spruce in Finland, well, I can see how this is a positive move. I have built saunas using t&g cedar without air gap and these saunas are still rocking 25 plus years later with no signs of moisture issues, so there you go. And i’m sure there’s lots to the other side of the air gap argument especially from Finland as, antidotally, that is the homeland, much like an Indian yoga instructor telling us it’s left foot over right for lotus position, not right foot over left!

    Foil bubble wrap:
    You can see the date I wrote this post. This was before Amazon was shipping, and before standard foil wrap was readily available with a couple mouse clicks. So, standard foil vapor barrier is easier to work with. You can overlap it, and it goes around corners with minimal profile. And it may have a higher service temp. rating than the foil bubble wrap (180°f.) that is available at big box.

    Sliding glass doors:
    Best advice I have for you is much along the lines of your thinking. Frame for it. Don’t calk your exterior trim, but set a couple of screws. Try your sauna. Get it rockin.’ If it works (in cold weather), then come back and calk and seal your exterior trim. If your sauna heater struggles like the little engine that couldn’t, then you can take out the big window and reframe, and chalk it up to “I tried!”.

    Hope this helps!

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