Hi, I’ve been experimenting with various setups on my mattress, which is a 7 year old Dr.s Choice from Denver Mattress. It’s been an OK mattress but started sagging this year; I opted to do a “foamectomy” mattress surgery and took out the worn out poly foam and added a 2 inch medium latex topper. That made a significant difference’. However, it still feels a bit too soft. I then tried the plywood between the foundation and mattress trick. I confirmed that the foundation is indeed a wire rod type foundation and not a box spring. That made for great support but maybe too much; I ended up with pressure point pain in my hips since I’m a side sleeper. My question is, even though the foundation is a rigid steel rod type that has virtually no give, adding plywood made the mattress feel MUCH firmer. The foundation does have gaps of up to 4 inches in the flat grid that the steel rods comprise; does the innerspring system sink down through those gaps and provide some softening to the mattress??? That is the only way I can think that the plywood made the mattress feel unbearably firm.
I’m assuming that you are referring to what I call a “wire grid” foundation that uses a rectangular grid of wires as the support surface. If putting plywood on top of your foundation made a difference that you can feel then it would either indicate that there was some flex or some sagging in the support system under your mattress that was affecting the feel and performance of the mattress or it could also be from your mattress sagging to some degree in between the gaps in the wire grid. Both of these would have been “corrected” with the plywood.
Wire grid platforms or foundations have a smaller load bearing surface area to support the mattress than wooden slats so the pressure is more concentrated in a smaller area and if the gaps in a foundation are larger than the diameter of the springs and there isn’t some “stiff foam” under the springs in the mattress or if the foundation doesn’t have some padding to make up for the gaps in the wire grid then the some of the springs would have less support underneath them and could sink a little more deeply into the gaps in between the wire grid surface which can lead to the heavier parts of the body “sinking down” a little more and feeling a little softer than they otherwise would.
Springs absorb very little energy so any flex or sagging under the spring or any sagging into any gaps will “travel” through the mattress much more easily than with foam materials that absorb and disperse more of the energy that comes from sleeping on the mattress than springs do.
If there is no remaining flex in your support system and the support surface doesn’t allow for any sagging into any gaps but your mattress now feels too firm then you could either replace the 2" latex layer with something softer or thicker or you could add an additional topper to your sleeping system to add the additional comfort and pressure relief that you need.
Yes Phoenix, it’s a wire grid style. In fact, I was able to get inside info that this foundation is made by Leggat and Platt. It looks like this: Error 404: Not Found - L&P Bedding Group
The L&P wire grid foundation you linked is a semi flex (which means it has some flex to it) and the plywood would have prevented any flexing in the foundation or any effects from the coils sinking slightly into any gaps in the support surface of the foundation or any effects from any sagging in the foundation … all of which could account for the change in the feel and firmness of your mattress.