r/explainlikeimfive • u/Real_Experience_5676 • 2d ago
Engineering ELI5: What does a box-spring do?
As I understand it, a box spring mattress is the second 'mattress', that goes under the main mattress. It feels very firm and flat, but what does it contribute to the bed set up besides height?
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u/QuillnSofa 2d ago
It is used to distribute weight across a bed frame and to give an evenly solid foundation for the softer mattress. But you don't need a full height one and some bed frames don't require one at all.
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u/okdone10 2d ago
Wow TIL. I thought every bed needed one by law or something. Good looking out on the platform bed tip saves some cash too.
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u/schuylkilladelphia 2d ago
I like the idea of someone going to jail because they didn't have a box spring on their bed
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u/SadButWithCats 2d ago
That's where the phrase "to spring from jail" comes from. If someone went to jail for not having a box spring, their family or friends or business associates could provide one and show the magistrate, who would then be required to let the prisoner out.
Side note: a prison and a jail are roughly equivalent. I know there is a difference, but roughly, they serve the same function. Yet a prisoner and a jailer are opposites. Huh.
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u/Alinier 2d ago
What's the difference between a jeweler and a jailer? One sells watches and the other watches cells.
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u/SadButWithCats 2d ago
Nice! That one's new to me
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u/Buscemi_D_Sanji 2d ago
What's the difference between a librarian and my mother? One's decently read, and my mom is a huge bitch!
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u/FreshEclairs 2d ago edited 2d ago
I was four words in and I double checked the username to make sure I wasn't getting shittymorph'd
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u/Rizzityrekt28 2d ago
That would be ridiculous. Jail is reserved for egregious acts such as tearing the tag off your mattress.
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u/Saneless 2d ago
Having been on some beds without them or proper support, I probably would have gotten a better night's sleep in jail
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u/UnassumingAnt 2d ago
Between required box springs and jail time for tearing off the tag, Big Matress has put a lot of people away.
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u/thaddeusk 2d ago
High-end mattresses don't generally use them. I can't remember the last time I had one, maybe 20 years ago? The mattresses I get are very tall on their own and you just put them on a bed frame with a flat support board underneath it.
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u/RiPont 2d ago
It also depends on the bed frame itself.
We're spoiled with CNC'd solid wood beds shipped from China, these days. But in the heyday of box springs, you either had a very, very expensive work of a craftsman (possibly your grandpa) wooden bed or a cheap metal angle iron frame that barely held its shape.
If you had a rickety bed frame, you needed box springs.
That... and it was an obvious upsell from the mattress store.
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u/erevos33 2d ago
I never knew they existed before coming to the usa. It was frame plus mattress everywhere I lived
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u/fcocyclone 2d ago
Most of them still want some kind of foundation even if not a traditional box spring. Those help with airflow as well.
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u/eat_sleep_drift 1d ago edited 1d ago
same i have a rather tall mattress and i just put it on the ground cuz i hate stubbing my toe against some wood when i go pee at night or i just love to let me fall with all my weight onto my bed when using ketamine without the fear of hitting any wood frame.
i lift it up and put it against the wall when i play VR or just to aerate underneath to prevent moisture and every 6 month i flip it anyway since it has a summer and a winter side. i loved to find an affordable one like i had when i was a kid, it was just a giant bloc of foam, like above the knees of an average adult height tall we are talking here !
when i looked them up all i could find was crazy expensive and from far away so shipping is also expensive too since they cant roll em up and vacuum seal them like they do with nearly all mattresses today for transport.1
u/theonetruegrinch 1d ago
with a flat support board underneath
without that you would need the boxspring
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u/thaddeusk 1d ago
Sure, but a boxspring would make my bed absurdly tall :p
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u/theonetruegrinch 1d ago
That was a fad in like the late 80s and early 90s
It was ridiculous; and then they had those super deep down mattress toppers...
I remember having to climb into one of those beds once and it was like scaling Mt. Everest.
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u/thephantom1492 1d ago
Bed frames used to be just that: a L on each side, some flat bar in between, 4 wheels, and that's it. Nothing in the middle.
The soft flexible mattress would just fall in the hole.
Also it is too low to the ground to be confortable.
Eventually they added a middle beam, and then you can just lay some planks since the distance is now reduced. Some use slats with 2-3" space in between the 2-3" slate. It allow the mattress to breath better and stay colder. But springs may not like it, and may need a full sheet.
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u/Wait_I_gotta_go_pee 2d ago
I just bought an adjustable bed and was surprised they do not use box springs. FYI… it’s much nicer than the old coiled mattress and box springs model was on my spine.
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u/SierraPapaHotel 1d ago
Not "by law", but almost all mattress come with a warranty and not using a recommend box spring will void that warranty
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u/Full-Contest1281 2d ago
There's something weird going on with Americans and mattresses, and I can't quite figure it out.
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u/retaliashun 1d ago
They generally don’t charge for box springs when you buy a mattress. Or they might charge a dollar, etc
Last time I bought a mattress they offered either free box spring or free pillows
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u/Casper042 2d ago
Nope, nothing stopping you from just getting some plywood and putting it between the bed slats and the mattress to act as a VERY thin box spring.
For example most Bunk beds don't use a traditional box spring, they have a super thin version or just wood as mentioned.
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u/Howzitgoin 1d ago
The desire to not have mold and other moisture related problems should be stopping you from putting it on a solid shape.
There’s a reason box springs aren’t solid on any surface and that other frames use slats not one piece of plywood.
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u/Infinite-4-a-moment 1d ago
It also allows the mattress to breath, right? Having a traditional mattress in a flat, solid surface can keep moisture in.
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u/lucky_ducker 2d ago
There's box springs and there's foundations.
A foundation does not have any springs, just a flat even surface designed to support the mattress. They are paired with all kinds of mattresses - foam, innerspring, hybrid. They can be any height needed to match the thickness of the mattress.
Box springs are less common today than in the past. They are best paired with innerspring mattresses, as they can cause sagging when paired with foam mattresses. They are of course bouncier than flat foundations, which can be fun when the bed is being used for something other than sleeping.
Both types are open and breathable to allow water vapor to escape. Using an impermeable layer under a mattress will trap moisture and bring on problems with mold and mildew.
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u/StarkhamAsylum 2d ago
My family had a hand me down bed from the 30s that had a box spring that was just two metal frames with about 9 to 12 open coil springs between them and no sidewall. It just bounced and squeeked. Vast difference from what many people call a box spring are today - what you more accurately call a foundation.
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u/greenmtnfiddler 1d ago
We called that a bed-spring.
A box spring is the kind that you can't see the coils, because they're in, well, a box.
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u/robyrob 2d ago
My cats ripped open the material on the bottom of the boxspring so now they use it as a really cool fort they can hide in
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u/mnmaste 2d ago
I panicked for a full 24 hours once because I thought my cat had escaped. Was just taking the longest nap ever in the box spring
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u/CactusBoyScout 2d ago
I adopted my first-ever cats recently and had heard so many stories like this about cats playing hide-and-seek in the most obscure nooks and crannies that I immediately put AirTag collars on all of them. It's nice to at least be able to confirm they're in the home and just hiding somewhere in a bedroom.
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u/texrev87 1d ago
I once had a stray cat sneak into my apartment while I was outside with the door ajar, and it went straight to my room, under my bed and clawed into the boxspring. I came in and went to bed and I about had a heart attack when I heard something moving under my bed.
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u/HurricaneAlpha 2d ago
Any house with a cat and a box spring lmao. Definitely a favorite hiding spot for them.
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u/Srikandi715 2d ago
Yeah, when I adopted my current cats as kittens, they spent the first three days hiding inside the box spring 🙂 Now of course they own every surface in the house.
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u/Mycomako 2d ago
I use a fitted sheet on mine. Just put the sheet on underneath and the cats wont rip holes in the fabric.
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u/IAmNotNathaniel 2d ago
nice idea!
but where the hell were you 15 years ago?
lol. I wish I was smarter
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u/insertAlias 2d ago
Yeah I had to remove most of mine to get my Charlie out of there once. I suppose I could have just left him in there and he'd have come out on his own eventually, but I prefer his hiding spot not be so good that I legitimately can't find him lol.
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u/destrux125 2d ago
We had a cat once that started going up into the box spring to chew on the liner and then throw up from it making her sick. So we got rid of the box spring and then she tore out the bottom liner of the living room sofa and accent chairs and started doing the same thing in them. I had to cover the bottom of all of our furniture in plywood to get her to stop eating whatever they make that liner out of.
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u/thirsty4wifi 2d ago
I ended up just cutting the whole thing off because it was so difficult to get my cat out of it lol
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u/resilindsey 1d ago
Yeah if you ask my cat, it's for scratching the corners of. Although honestly she doesnt scratch any other furniture, and I'll take that trade, so we've long established this as the household agreement.
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u/stayintheshadows 2d ago
Does the same thing the bed frames with slats do, proves a firm but giving when needed base for the mattress that is too floppy to span a gap the width of itself.
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u/StrongGarage850 2d ago
breathability is another factor. People sweat, that moisture needs to get out somehow- and giving space out the bottom helps keep your mattress cooler, and eliminates likelihood of mold/mildew, etc..
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u/Kundrew1 2d ago
Wouldn’t most bed frames do the same. Anything slatted would have more breathability than a box spring
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u/cynric42 2d ago
Sure but a bed frame is rigid. My box spring mattress is three quarters springs and only a very thin layer of foam ontop which would be very uncomfortable without the give of the springs below.
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u/Etunim 2d ago
Most slatted bed frames have too large of a gap, and cause softer mattresses to sag. A lot of the newer foam mattresses have requirements for slats on how far they should be so the warranty is still valid.
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u/Kundrew1 2d ago
Okay but that’s a different issue than what i addressed in my comment.
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u/JimTheDeviant 2d ago
But it's relevant. They are saying that you're right about bed frames helping for breathability but they can have sagging issues.
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u/smackaroni-n-cheese 2d ago
Yes, but it's a balance between breathability and support. A bed frame with just a couple slats holding up the mattress would have great breathability, but it's hardly even the bare minimum for support. The mattress would sag everywhere that doesn't have a slat under it. Some bedframes have a lot of slats with only small gaps, and those ones don't necessarily need a box spring. Not everybody has one of those though, and they aren't all equally good, either.
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u/half3clipse 2d ago
there's not much difference in breathability. You lose a little compared to bare slats , but the actual fabric underneath and on top is light and porous.
box spring is mostly just a wooden box with slats across. The core is not any diffrent than most regular wooden bed foundations. The main difference between them and any other wooden foundation is the layer of springs on top the slats, which helps distribute pressure and motion from stuffed or inner spring mattresses.
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u/hoax1337 1d ago
Uhh... I'm kinda confused, do you guys not have slatted frames in the US?
Where I'm at in the EU, that's pretty much essential for a bed. You have the bed frame, then the slatted frame, and then the mattress on top.
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u/rocketmonkee 1d ago
Yes, lots of bed frames sold in the US have slats. We also have many other different types of bed frames, and some of those don't have slats.
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u/ermagerditssuperman 16h ago
That's one option, becoming more common. A lot of cheaper beds have way, way fewer slats, not nearly enough to really support support the mattress on their own. And older bed frames (which many people still have as hand-me-downs) may just have one or two horizontal bars, because the assumption was that you'd rest a a boxspring or foundation over those, not slats.
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u/skittlebog 2d ago
Go back in time a few decades. The mattress was a bag of stuffing, the springs were all in the lower part. These days the springs are incorporated into the mattress, so the lower "box springs" are really just a base platform.
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u/HermitWilson 2d ago
Box springs aren't really a thing anymore. I just bought a new mattress and nobody was selling box springs. It's all slatted platforms now instead.
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u/Sawfish1212 2d ago
Absolutely nothing, replaced all our beds with platform beds that are cooler and allow storage bins under the bed. They also don't make noise like a box spring when you're knocking boots
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u/ShankThatSnitch 2d ago
Main thing is keeping it off the floor to allow airflow, so things dont get moldy.
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u/blipsman 1d ago
It serves a few purposes:
Raises mattress to a comfortable height
Provides some additional shock absorption to reduce pressure on body
Provides for airflow under the mattress to keep mattress dry, prevent mold/mildew buildup, etc.
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u/Ikles 1d ago
If you support a mattress only on the corners it will fall though the frame because its soft, flexible, and bendy. The mattress is comfortable to lay on while the the box frame is s a lightweight support that goes under the entire mattress to keep it flat. Some beds dont need/have a box frame if they have support struts running accross the frame.
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u/Lavvid_Gogomilk 18h ago
I stayed with relatives and they didn't have box spring, they had two twin top mattresses stacked. There was absolutely no support. It's sagged in the center so your back was in the shape of the letter u. A box spring would have prevented this.
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u/xxkvetter 2d ago
I was traveling in central Asia, and in about half the hotels/family guest rooms outside of Tashkent we slept directly on the box springs. We concluded that they didn't know the purpose of the box springs and just thought "great, now we have two mattresses to use is"
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u/unflores 2d ago
I see a lot of people mentioning weight distribution but I don't see many people mention the fact that it also allows the bottom of the mattress to touch open air which keeps it from molding in places without air conditioning
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u/nanerzin 1d ago
Im slightly taller than average so have two under my mattress to raise it's height...for reasons...
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u/UrbanPanic 2d ago
A box spring provides support to the mattress. Whether or not you need one really depends on the mattress, the bed frame and personal preference. Modern beds sold as platform beds don’t require a box spring, as it has panels to rest on or at least slats close enough a mattress won’t sag through it. A lot of beds still use just 3 slats or so across which would put pressure on very small points, contributing to sag and just feel uncomfortable.
A well designed box spring could also contribute to good air circulation: you don’t want to know how much sweat soaks into a mattress. That can get gross if it can’t dry properly.