Sealing method, and what that means for contact between the sample and the liquid nitrogen.
The Sealing Difference
CBS High Security sperm straws seal at both ends and keep the sample isolated from the liquid nitrogen throughout storage. They come in 0.3 ml and 0.5 ml and seal with the SYMS or SYMS III sealer. Embryo straws are 0.15 ml and 0.3 ml.
Why Isolation Matters
The ASRM and SART Practice Committees, writing on cryostorage in Fertility and Sterility (2020;114:486-491), note that liquid nitrogen is not sterile and can carry viable organisms between samples in a shared vessel. Closed straws remove that route at sample level.
Documented transmission in clinical practice is vanishingly rare, so the trade is a small reduction in cooling rate against a low probability risk. Both positions are defensible. An undocumented position is not, and it is the first thing an inspector will ask about.
The Compatibility Point
Sealing requires a matched sealer, and the sealer has to suit the straw. Plan one per freezing station plus spares, because a shared unit is a bottleneck on a busy day and a single point of failure on a bad one. See the full chain in cryogenic straws, canes and goblets.
