MUHWA 5mL Cryo-Safe Freezing Container — 12-Place, Isopropanol Cooling Bath
If you freeze down cell lines regularly, you know the drill: resuspend your pellet in freezing medium, aliquot into cryovials, load them into a container with isopropanol, and transfer to -80. Come back the next morning and move the vials to LN2. This container does exactly that. It holds 12 tubes (1.0 to 5.0mL cryovials — the internal rack is stepped to grip different diameters) and uses a room-temperature isopropanol bath to deliver controlled-rate cooling at roughly 1 degree C per minute.
The polycarbonate body won't crack in the -80, and the HDPE screw closure keeps the isopropanol smell contained. The rack inside is removable — pull it out if you need to clean it or if you're switching between different tube sizes and want to position things differently. No electronics, no programming, no LN2 phase to manage. Fill to the line with isopropanol, load your tubes, close the lid, and put it in the -80.
How to Use It
First time setup. Fill the chamber with 100 percent isopropanol to the fill line marked inside. That's your cooling bath — it stays in the container between uses. The isopropanol doesn't need to be fresh every time, but top it up if the level drops from evaporation. Replace it every 3-6 months or if it picks up color or odor from repeated freeze-thaw cycles.
Freezing protocol. Pre-label your cryovials. Resuspend your cell pellet in cold freezing medium (typically 90 percent FBS + 10 percent DMSO, or your lab's formulation). Aliquot into vials, cap tightly, and place in the rack inside the container. The isopropanol should be at room temperature when the vials go in — if it's pre-chilled, the cooling rate will be faster than expected. Close the HDPE lid. Transfer the entire container to a -80 degrees C freezer. Leave overnight (minimum 4 hours). The next day, transfer vials directly to liquid nitrogen for long-term storage.
What the isopropanol actually does. Isopropanol has a thermal conductivity and heat capacity that, in a closed container at -80, produces a cooling curve of about 1 degree C per minute across the critical range (4 degrees C down to roughly -30 degrees C). That's slow enough that intracellular ice crystals don't form and fast enough that the cells don't sit in hypertonic medium for too long. The exact cooling rate depends on your freezer model and the starting temperature of the isopropanol — if you want to verify, put a thermocouple in a dummy vial of freezing medium and log the curve once.
Between uses. Take the container out of the -80, let it warm to room temperature (the isopropanol will thaw — it stays liquid to about -89 degrees C anyway, but it gets thick and syrupy at -80). Check the fill level. Load your next batch of vials and go again. If the isopropanol level has dropped noticeably, top it up. If it looks cloudy or has debris, drain and replace.
Specs at a Glance
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|---|
| Tube capacity | 12 positions, fits 1.0-5.0mL cryovials |
| Container body | Polycarbonate |
| Closure | HDPE screw cap |
| Cooling medium | 100 percent isopropanol (not included) |
| Cooling rate | Approximately 1 degree C/min (freezer-dependent) |
| Operating temperature | Room temp to -80 degrees C (container); vials go to LN2 after freezing |
| Rack | Removable, stepped for multi-size tube grip |
Questions That Come Up
Do I really need isopropanol, or can I use ethanol?
Use isopropanol. Ethanol has different thermal properties — the cooling curve won't be 1 degree C/min and your recovery rate may drop. The protocol that works for most labs was optimized with isopropanol. If you must substitute, test with a sacrificial vial and a thermocouple first.
How often do I change the isopropanol?
If you're freezing cells weekly, replace every 3-6 months. If you use it less often, once a year is enough. Replace sooner if the isopropanol picks up color, develops an odor, or has visible debris. Evaporation loss is normal — just top up to the fill line.
Can I leave the vials in the container in the -80 long-term?
You can, but the better practice is to transfer to LN2 the next day. The container is a freezing device, not a storage device. Long-term -80 storage in the isopropanol bath risks the alcohol becoming contaminated and eventually leaking into poorly sealed vials. Move your vials to a cryo box for LN2 storage after the overnight freeze.
What cell types does this work for?
Standard mammalian cell lines: HEK293, HeLa, CHO, NIH/3T3, Jurkat, hybridomas, iPSCs (most lines — check your protocol for ROCK inhibitor supplementation during recovery). Primary cells are trickier — they're more freeze-sensitive and some benefit from a slower ramp using a programmable controlled-rate freezer. Test a pilot batch before committing your entire precious primary cell stock.
The lid is stuck after freezing. Help?
The HDPE contracts more than polycarbonate at -80. Don't force it — you'll crack the threads. Run warm (not hot) water over the lid for 15-20 seconds. It'll loosen. Next time, apply a thin film of silicone grease to the threads before freezing.
