A dry shipper is an insulated cryogenic flask/container that contains refrigerated liquid nitrogen absorbed into a porous lining. It is used to transport specimens.
Quantity limits: N/A
The liquid nitrogen must be completely absorbed into the container lining; there must be no free liquid.
Container must not allow the buildup of pressure.
Liquid nitrogen must not escape from the package regardless of the package orientation.
See the regulation: 49 CFR 175.10(a)(23)
Tip: It is normal to sometimes see vapor coming from these containers as they must allow the escape of gaseous nitrogen.