rigid
adjective
incapable of or resistant to bending
“a rigid strip of metal”
“a table made of rigid plastic”
Synonymsstiffincapable of compromise or flexibility
Synonymsstrictincapable of adapting or changing to meet circumstances
“a rigid disciplinarian”
“an inflexible law”
designating an airship or dirigible having a form maintained by a stiff unyielding frame or structure
Oppositesnonrigidfixed and unmoving
“with eyes set in a fixed glassy stare”
“his bearded face already has a set hollow look”
Source: WordNet 3.1, Princeton University