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As I understand it, foam blocks have a property called firmness, which is essentially, for a given % of height reduction, how much force does it take to achieve it. Firmness is measured using the force in kg necessary to reduce a foam sample of a specific height by 25% of it's original height, a measurement termed Indentation Force Deflection (IFD).

Suppose we had two foam blocks of different thicknesses, which are, apart from the thickness, identical. By thickness I mean, if you place them on a table, the thicker foam block has a greater height from the surface of the table than the less thick foam block.

My question is, does thickness affect the compressibility of the foam? Will having more foam make it harder to compress? If so, why?

This intuition came to me because I recalled, if I take a single piece of paper, it will tear quite easily if I rip it in half. But if I take an entire ream of paper, it will not tear easily and be much harder. So I was wondering whether a similar property existed here.

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  • $\begingroup$ tearing multiple sheets is like compressing a large foam block to the same height as a small block, not compressing to a percentage of height $\endgroup$
    – jsotola
    Dec 29, 2022 at 19:29
  • $\begingroup$ The fact foam compression is measured by percentage answers your question. What you need to clarify in your mind is what you are really thinking about when you think "harder to compress". Whether you mean compressing thicker foam by the same distance as the thinner foam or by the same percent thickness. From there everything can be converted to a percentage thickness to find the force required. $\endgroup$
    – DKNguyen
    Dec 30, 2022 at 2:34

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Foam "compressiblity" as you expressed it is a percentage of compression, so any thickness will be the same.

Tearing multiple sheets of paper is completely different, this is more like putting several boards together to make them stronger.

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