Borosilicate glass. Designed for use with rotary and reciprocating shakers where baffle indents provide greater turbulences to improve oxygen transfer rates or aeration. Flask has a neck with a plain fire-polished finish and is suitable for a plastic cap etc. Borosilicate glass. Designed for use with rotary and reciprocating shakers where baffle indents provide greater turbulences to improve oxygen transfer rates or aeration. Flask has a neck with a plain fire-polished finish and is suitable for a plastic cap etc.