What gas is typically used to fill suit bottles along with argon?

Argon is commonly used to fill dry suit inflation bottles due to its properties as an inert gas that provides thermal insulation and does not contribute to buoyancy issues. Additionally, helium is sometimes mixed with argon in these suit bottles. Helium is used for its low density, which can enhance thermal insulation and help reduce thermal conductivity when divers are in cold-water environments. This mix improves the insulating properties of the dry suit and provides the diver with confidence in maintaining warmth during extended dives in cold waters.

The other gases listed—nitrogen, hydrogen, and carbon dioxide—are not typically used for this purpose because they do not provide the same benefits as helium and argon. Nitrogen can contribute to buoyancy and is not as effective in providing thermal insulation as helium. Hydrogen, while it has certain characteristics, is not safe for use in underwater environments due to its flammability. Carbon dioxide could lead to issues such as buoyancy control and does not have the insulating characteristics beneficial for dry suit divers.