Word to describe object that can be physically passed through

Borrowing from Carl Sagan's The Dragon in My Garage, which suggests this word for specters:

incorporeal - having no physical body or form

(Definition from Merriam-Webster.)

I have to take issue with permeable. A sieve is permeable, a sponge is permeable, but unless you're a molecule or a virus or something similarly small you can't pass through.

How about ethereal or penetrable?

M-W:

ethereal: lacking material substance

penetrable: allowing someone or something to pass through or enter : able to be penetrated

It's not hard to imagine passing through anything ethereal.

It would not be unreasonable to consider a ghost, gas, or mist penetrable, in fact infinitely so.

Note: @Drew mentioned penetrable in a comment.

The word you're looking for is permeable.

Ghosts are permeable, a gauze curtain is permeable, a cloud is permeable.

Permeable

allowing liquids or gases to pass through