I can't remember if I last used Express or Priority. I think it was Priority...Either way, they're put into 12 oz soda bottles that I rinse out thoroughly with water. I fill these bottles with dechlorinated water to the top of each bottle. The bottles are then bagged, and placed inside a box (Styrofoam for Express, or a Priority shipping box) lined with bubble wrap. I also make sure to notify the postal service that what I'm shipping is fragile and temperature sensitive.