Editing Luffa (section)

===Fiber-bundles===
[[Tensile testing|Uniaxial tensile tests]] of fiber bundles isolated from the inner surface provide insight this basic [[strut]] element of the luffa sponges. These fiber bundles vary in [[diameter]] from 0.3 to 0.5&nbsp;mm.<ref name=":0" /> Each fiber bundle has a low density core region not occupied by fibers.<ref name=":1">{{doi|10.3390/ma10050479 }}</ref> The [[Stress–strain curve|stress-strain]] response of the fiber bundles is nearly [[Linear elasticity|linear elastic]] all the way until [[fracture]], suggesting the absence of [[work hardening]]. The [[slope]] of the [[Linearity|linear]] region of the stress-strain curve, or [[Young's modulus|Young’s modulus]], is 236* MPa. The highest stress achieved before fracture, or [[ultimate tensile strength]], is 103 MPa. The strain at which failure occurs, or failure strain, is small at only 5%. The mechanical properties of fiber bundles decrease dramatically when the size of the hollow region inside the bundle increases.  Despite their low tensile strength, the fiber bundles have a high [[specific modulus]] of 2.07– 4.05 MPa⋅m<sup>3</sup>/kg, and their overall properties are improved when a high ratio of their cross sectional area is occupied by fibers, they are evenly distributed, and there is strong adhesion between fibers.<ref name=":0" /><ref name=":1" />