An invisible thing can't be seen, but what do you call something which cannot be smelled?
Inolfactible. Olfactible is in the O.E.D.
An odour is a smell.
You'd need some context to make this work, but I rather like
(meaning that something can't be perceived by the senses or a sensor)
unscented, means it hasn't had any scent added.
clean, means they're recently washed.
inert, means it's unreactive and won't stimulate those nerve-endings.
3 : deficient in active properties; especially : lacking a usual or anticipated chemical or biological action
odourless, (odorless) free of odour