As nouns the difference between firmness and durability
is that firmness is the state of being firm; strength; permanence; stability; hardness; resolution while durability is permanence by virtue of the power to resist stress or force.
firmness
English
Noun
The state of being firm; strength; permanence; stability; hardness; resolution.
References
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durability
English
Noun
(durabilities)
Permanence by virtue of the power to resist stress or force.