(a.) Not elastic.

adamant adamantine cast-iron dour firm flinty grim hard hard-core immovable immutable implacable impliable inductile inexorable inextensible inextensile inextensional inflexible intractable intractile intransigent iron irreconcilable irresilient nonelastic nonstretchable relentless rigid rigorous rock-ribbed steely stern stiff stubborn unaffected unalterable unbending unchangeable uncompromising unextendible unextensible unflexible ungiving unlimber unmalleable unmoved unpliable unpliant unrelenting untractable unyielding