What Is the Difference Between an Onion Dewar and a Modern Cryogenic Storage Vessel?

The onion dewar and the modern cryogenic storage vessel perform the same function – maintaining biological samples in liquid nitrogen at -195.8 degrees C – but differ significantly in capacity, evaporation efficiency, canister configuration, and neck design. For an IVF laboratory carrying a growing sample inventory under HFEA storage limits that now extend to 55 years, these differences have direct operational consequences.

How does the neck design differ?

The onion dewar typically features a narrow neck and a distinctive rounded outer casing. The narrow neck limits both the number of canisters the vessel can accommodate and the ease of access during sample retrieval. Modern cryogenic storage vessels use a wider neck design that accommodates more canisters, allows full-size cryocane access without excessive reach depth, and typically provides better insulation performance at the neck – historically the point of greatest heat ingress.

How does canister capacity compare?

A standard onion dewar typically accommodates three to five canisters. Modern mid-range storage vessels accommodate five to six canisters as standard, with large-format vessels accommodating more. For a laboratory storing embryos under the 55-year Health and Care Act 2022 limit, canister capacity directly affects how many samples can be held in a given floor space – which has real implications for laboratory planning.

Is the liquid nitrogen evaporation rate better in modern vessels?

Yes. Improved vacuum insulation technology and optimised neck geometry in modern storage vessels result in lower static evaporation rates than most onion dewar designs. Lower evaporation rates mean lower liquid nitrogen running costs, longer hold times between top-ups, and greater resilience during nitrogen supply disruption.

Moving from an onion dewar to a modern storage vessel is not an upgrade in principle – it is an upgrade in operational performance. The samples do not know the difference, but the laboratory managing them does.

Cryolab supplies modern cryogenic storage vessels to replace legacy onion dewars. Contact cryolab.co.uk/contact-us/ for a capacity recommendation.