Hey there!
I'm current investigating some possible alternatives to using cotton as a stopper for the water side of the test tube in claustral tubes for my Camponotus queens.
As it stands, I can only think of a few choices:
1. Wadded up denim or cotton cloth
2. A non-treated kitchen sponge of some kind.
3. A PVA sponge.
Has anyone tried any of these or have any experience or thoughts?