As adjectives the difference between smellable and swellable
is that smellable is that can be detected by smell while swellable is that is capable of swelling.
smellable
English
Adjective
(-)
That can be detected by smell.
References
* 2007', Günter Radden, René Dirven, ''Cognitive English grammar'', page 284: "Conversion predicates of perception tend to be coded as adjectives: ''visible'', ''audible'', ''palpable'' and ''tangible'', but English lacks adjectives such as '''''*smellable'' and ''*tastable for something that can be smelled or tasted."