Let’s Talk About Foam Properties

Beyond Mattresses
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Hi TMU. I’m hoping you can help me expand my vocabulary when talking about the properties of different foams. I have at least a conceptual understanding of foam density and ILD, but those don’t quite describe the comfort properties of foams.

In my personal experience, I have two different layers that I’ve primarily been playing with - 2” Serene foam and 2” medium Dunlop latex. I would describe both of these as “comfortable” even thought they are very different. I’d like to learn how to describe the differences more appropriately.

Firmness/Softness - This is where I think the ILD comes into play. I think the medium latex is somewhere around 30. I don’t know the ILD of the Serene, but it is very soft so I would guess significantly under 20. This measurement feels somewhat intuitive to me.

Pinching or pushing in with fingertips - With the Serene, I can easily pinch all the way through the 2” layer and feel my fingertips touch each other - it’s effortless. Same with pushing down into the layer with either a closed fist or my fingertips - I can easily feel the floor or whatever is underneath through the layer. The Latex is different here - it’s more of a progressive resistance, I’d say - the deeper I pinch or push into it, the more firmly it pushes back. It’s like the Serene gets out of the way and the Latex stands its ground, if that makes any sense. What is this property called? How is it measured?

“Bouyancy”(?) - I don’t know if that’s the right term, but it’s something I notice specifically with the Serene. I can easily push into it as described above, but when I lay my whole body on it, I “float”. My hips or shoulders sink into it pretty good, but overall it holds my body up - it doesn’t just flatten out or get out of the way like it does when I pinch it. Similar to the way I can push my hand or whatever easily into water, but I can also lay on the surface and float. I know that’s because of the surface tension of the water, but what is in play with the Serene? The latex is not like that - the progressive resistance seems consistent whether I push in with my hand or whether I lay my whole body on it. What is this property?

There are other interesting differences between the two materials, but that’s enough for now. Can you help me learn some new terminology and ways of describing these properties?

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Hi cmyoung19!

You’re asking some great questions and I love how clearly you’ve described your personal observations. This is such a good way to approach learning how to articulate the more subtle “feel” properties of different materials beyond just density and ILD.

You’re totally right that ILD gives you a general sense of initial firmness/softness (how much force it takes to compress the foam a certain percentage), but there are several other factors that come into play with comfort and support characteristics. Let’s break down a few of the things you mentioned:

1. Progressive resistance / how the material “pushes back”
What you’re describing when the latex offers more resistance the deeper you push is often referred to as support factor or compression modulus. It’s essentially how the material responds as you go beyond initial compression - does it stay soft, or does it firm up quickly? Latex tends to have a high support factor, which is why it “stands its ground” the deeper you compress it. Foams like Serene often have a lower support factor, so they don’t push back as much once you’ve started sinking in.

2. Ease of “pinch” or compression with fingers vs. whole body
This touches on what some call point elasticity - how well a material compresses under a specific area of pressure without affecting the surrounding areas. Latex typically has high point elasticity, meaning it compresses locally but doesn’t create a “crater” effect around the pressure point. Serene, being more conforming and with lower support factor, tends to have a more distributed response.

3. “Floating” sensation on Serene vs. consistent pressure on latex
I think you’re spot on using the word buoyancy, and that’s actually a pretty common term in the mattress world too! It refers to how quickly and strongly a material pushes back and lifts you up. Latex is known for its buoyant feel, fast response, springy, elevating. Serene’s floating sensation might be due to its pressure distribution properties, it allows localized sinking but still holds your full body fairly evenly, likely due to its viscoelastic characteristics mixed with polyfoam traits.

4. Response / recovery
You didn’t name it, but your description implies differences in how quickly the materials rebound after compression. This is usually called resilience or response time. Latex = high resilience/fast recovery. Serene = more of a dampened, slow-ish return depending on blend.

Hope this helps expand your vocabulary a bit! Let me know if you want to explore others like hysteresis, damping, or temperature sensitivity. You’re doing an awesome job putting language to feel…which is honestly half the battle in mattress design and selection.

NikkiTMU

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Thank you for this response, very helpful. I’m hopeful that when discussing mattresses, I can move beyond simply saying “it’s too hard/soft”, or “it’s comfortable/it’s terrible”! Additionally, I think it can help to anticipate what unknown materials may feel like. Especially in the area of newer advanced polyfoams - names like Serene, Energex, LoftAdapt, HyPURGel are great for marketing, but don’t really provide much insight into the pressure relief or support properties of the materials.

You mentioned temperature sensitivity, and I’ve seen that term used fairly frequently. What is your take on that in relation to mattress attributes?