What are inelastic elastic-bands? In the third episode of Julius Sumner Miller's physics series he sets up an experiment with two masses connected by an array of elastic-bands. 
He comments that the elastic-bands are inelastic. 
What did he mean by this?
 A: Inelastic conventionally means that the material deforms or relaxes permanently under a load (as opposed to recovering completely when the load is removed, which characterizes elasticity).
Actually, all materials are strictly inelastic, as some degree of viscous flow is inevitable at any nonzero temperature even in solids. For the typical engineering materials around us, this flow is negligible. 
One form of inelasticity is the deformation over time in a solid under load, called creep and perfectly exhibited by these lead pipes that sagged over decades:
Frost and Ashby: http://engineering.dartmouth.edu/defmech/Chapter_19.htm.
I can think of a couple possibilities for interpreting what Miller said:


*

*He might have been emphasizing the greater susceptibility of elastomers to creep, as they contain relatively few crosslinks, or strong bonds connecting adjacent polymer chains. As a result, elastomers exhibit more prominent inelastic behavior (e.g., stress relaxation, creep, and hysteresivity) than, say, metals or ceramics or thermoset polymers (that is, heavily crosslinked polymers).

*It's also possible that he misspoke, rather meaning that rubber bands are nonlinearly elastic (which of course would eliminate the elastic-inelastic aside). A notable property of elastomers is that their stress-strain diagrams contain barely any section of linear elasticity; this behavior arises because the stiffness of an ideal elastomer arises entropically (via straightening of polymer chains) rather than through bond stretching (which is termed enthalpic stiffness).In other words, elastomers obey Hooke's Law over only relatively small fractions of their stress-strain diagrams, if at all. Here's the stress-strain diagram of a rubber composite, for instance; as we uncoil and unkink the polymer chains and straighten the strongly bonded backbone, the curve steepens, indicating increasing stiffness:Das, Amit, et al. "Nanoalloy Based on Clays: Intercalated‐Exfoliated Layered Silicate in High Performance Elastomer." Journal of Macromolecular Science, Part A: Pure and Applied Chemistry 45.2 (2008): 144-150.Despite this nonlinearity, we might treat rubber bands as elastic objects as long as the time scale isn't too long and the temperature isn't too high. But we could always test this assumption: does the stress-strain unloading curve follow the loading curve exactly? If not, hysteresivity—a type of inelasticity—has occurred.
I watched only the few seconds of the video that included the "elastic-inelastic" aside. Perhaps Miller says something elsewhere in the video that clarifies which interpretation is correct.
Since you've watched more of Miller's presentations, which possibility seems most likely to you?
