Do I have a box spring or a foundation?

Hi all,

First post here.

I’m doing some research into buying a new mattress, which has led me to trying to understand what I currently own. All of the current beds in our house were either bought second-hand or were picked out at the store without a lot of consideration. This will hopefully be different for our next mattress. :slight_smile:

My wife and I are currently sleeping on a mattress that we got second-hand as part of buying a complete set of bedroom furniture from a couple who was moving to Japan. After looking it over I’m not sure whether what we have on the bottom is a foundation or a box spring, or whether it would be suitable to use underneath a new latex or foam mattress. (I know the ideal would probably be to buy a completely new foundation, but I don’t know if our budget will let us do that all at once).

The construction of this unit has a wooden frame around the bottom perimeter. The top surface is a grid of metal wires spaced approximately 2" apart, covered with a thin layer of padding and fabric. The top surface is supported above the wooden frame by wires that periodically zig-zag from the grid to the wood and then back. (In case it matters, there are actually two supporting units under the king-sized mattress, each twin-xl in size).

So, I’m not sure what this actually is? I don’t think it is a box spring since there are no coil springs inside it, but it doesn’t seem right to call it a foundation since it is “springy” and does compress if you push down on it.


Hi rialto,

It sounds to me (based on your zig zag description) that you have a box spring that uses torsion bars similar to (these or to these) instead of a coil spring (like these) inside. All of these are examples of box springs which are designed to “give” under pressure which is the basic difference between a box spring and a foundation which is designed to be rigid and not have any flex at all. If yours flexes when you press down with your knee or with any firm pressure … then it is a “box spring”.


Thanks for those links. I’m going from memory right now since I’m not at the mattress, but I think the “Semi-Flex” is the best match for what it looked like. I’ll have to take another look to be sure.

The description of Semi-Flex doesn’t make it easy:

Seems like they want to call it a foundation -and- a box spring. But based on your explanation it seems like it is just a kind of box spring, no?

Hi rialto,

Yes … it is a “box spring” that has flex (you would be able to compress it with your knee or firm pressure).

Sometimes people use “foundation” as a generic term which can mean “anything under your mattress” which provides the foundation that your mattress sits on rather than the more specific use of the word (a rigid non flexing surface). You will also sometimes see something called “box spring foundation” which is also a box spring used as the “foundation” of your mattress.

Confusing I know … just like so much else connected with mattresses and some “mixed up” terminology :slight_smile: