This method uses straws and has the following advantages:
-Economies of space (5-6 straws can be stored in each cryotube).
-Prevention of seepage of liquid nitrogen into the samples; liquid nitrogen may penetrate the washers of polypropylene cryotubes, but cannot penetrate the sealed straws.
-Polypropylene drinking straws are cheap and readily obtainable throughout the world.
-Polypropylene is very much safer to use than glass vials.
-The straws are available in different colours, allowing colour-coding of samples.
-The culture can be recovered for use by removal of a single straw, the rest of the samples remaining frozen.