Editing Memory foam (section)

== Mechanics ==
Memory foam derives its [[viscoelastic]] properties from several effects, due to the material's internal structure. The '''network effect''' is the force working to restore the foam's structure when it is deformed. This effect is generated by the deformed porous material pushing outwards to restore its structure against an applied pressure. Three effects work against the network effect, slowing the regeneration of the foam's original structure:
* The '''pneumatic effect,''' caused by the time it takes air to flow into the foam's porous structure.
* The '''adhesive effect''', or [[adhesion]], caused by the stickiness of the surfaces within the foam, which work against decompression as the internal pores within the foam are pressed together
* The '''relaxation effect''' (the strongest of the three forces working against expansion), caused by the foam's material being near its [[glass transition temperature]]—limiting its mobility, forcing any change to be gradual, and slowing the expansion of the foam once the applied pressure has been removed

The effects are temperature-dependent, so the temperature range at which memory foam retains its properties is limited. If it is too cold, it hardens. If it is too hot, it acts like conventional foams, quickly springing back to its original shape. The underlying physics of this process can be described by polymeric [[creep (deformation)|creep]].<ref name="autogenerated1">{{cite web |last1=Krebs |first1=Michael |title=The Adjustment of Physical Properties of Viscoelastic Foam – the Role of Different Raw Materials |url=https://www.pu-additives.com/product/pu-additives/downloads/adjustments-of-physical-properties.pdf |website=pu-additives.com |access-date=21 May 2020 |archive-date=6 July 2020 |archive-url=https://web.archive.org/web/20200706205344/https://www.pu-additives.com/product/pu-additives/downloads/adjustments-of-physical-properties.pdf |url-status=dead }}</ref><ref>{{cite web |last1=Landers |first1=R |title=The Importance of Cell Structure for Viscoelastic Foams |url=https://www.pu-additives.com/product/pu-additives/downloads/importance-of-cell-structure-for-viscoelastic-foams.pdf |website=pu-additives.com |access-date=21 May 2020 |archive-date=6 July 2020 |archive-url=https://web.archive.org/web/20200706115736/https://www.pu-additives.com/product/pu-additives/downloads/importance-of-cell-structure-for-viscoelastic-foams.pdf |url-status=dead }}</ref>

The pneumatic and adhesive effects are strongly correlated with the size of the pores within memory foam. Smaller pores lead to higher internal surface area and reduced air flow, increasing the adhesion and pneumatic effects. Thus the foam's properties can be controlled by changing its cell structure and [[porosity]]. Its glass transition temperature can also be modulated by using additives in the foam's material.<ref name=autogenerated1 />

Memory foam's mechanical properties can affect the comfort of mattresses produced with it. There is also a trade-off between comfort and durability. Certain memory foams may have a more rigid cell structure, leading to a weaker distribution of weight, but better recovery of the original structure, leading to improved cyclability and durability. Denser cell structure can also resist the penetration of [[water vapor]], leading to reduced weathering and better durability and overall appearance.<ref>{{cite journal |last1=Scarfato |first1=Paola |last2=Di Maio |first2=Luciano |last3=Incarnato |first3=Loredana |title=Structure and physical-mechanical properties related to comfort of flexible polyurethane foams for mattress and effects of artificial weathering |journal=Composites Part B |date=16 October 2016 |volume=109 |pages=45–52 |doi=10.1016/j.compositesb.2016.10.041 }}</ref>