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What is the name of the property that materials like cloth have that allows it to be bent or folded on itself without any significant elasticity, but also not permanently deformed either? Softness? Ductility? Bendable? Deformable?

On a molecular level, what is it that gives materials this quality? Is it because of weak bonds? Or a certain arrangement of the molecules?

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  • $\begingroup$ I think softness and elasticity are not the same thing. $\endgroup$
    – Roger V.
    Apr 15, 2020 at 13:26
  • $\begingroup$ @Vadim I don't see any mention of elasticity here. $\endgroup$
    – JMac
    Apr 15, 2020 at 13:37
  • $\begingroup$ @JMac you are right, bending can mean several things. $\endgroup$
    – Roger V.
    Apr 15, 2020 at 13:44

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The precise technical term—the opposite of stiffness, and the quality of easy recoverable deformation—is compliance.

Yes, a compliant material is sometimes also referred to as "bendable" or "flexible" (if you're bending it) or "deformable" (although this can refer to either recoverable or nonrecoverable deformation).

"Elasticity" is ambiguous; some researchers use it to refer to compliance and some to stiffness. The term is therefore perhaps best used to describe the general topic and study of recoverable deformation, without a specific link to either compliance or stiffness.

"Soft" and "ductile" refer to nonrecoverable deformation.

On a molecular level, what is it that gives materials this quality?

The key property is that there's very little energy penalty associated with deformation. This may mean that the bonds are weak (in which case the material may be both compliant and soft). But it could also mean that the geometry is such that a great deal of deformation can be obtained from bond stretching (this is the case for thin parts or for stretching of elastomeric polymer chains, for example).

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Flexibility and pliability are words that have been applied to textiles, but to be quite honest this seems like a question in textile engineering, not in physics

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  • $\begingroup$ Those words are basically what I meant I think, though Wikipedia defines flexibility as elasticity. I'm going to see if another site can help or elaborate $\endgroup$
    – Curtwige
    Apr 15, 2020 at 21:16
  • $\begingroup$ That looks like an error in Wikipedia, if follow the link it defines flexibility as the opposite of stiffness and specifically states that a low modulus of elasticity is needed for flexibility $\endgroup$ Apr 15, 2020 at 21:37
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The Young's modulus, which is the comprensive stiffness of a material when a force is applied lenghtwise. From the Young's modulus you can find the Bending Stiffness, which is the resistance of a material against deformation.

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I think the term you're looking for is viscoelastic. As for the molecular characteristics, I would think it does depend on the material; for example, a rubber sheet may exhibit this characteristic, but the driving force back towards its original properties is an entropic driving force, not the molecular bonds.

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