The temperature range of the material of the tubes, caps and racks is approved from -80ºC to +100ºC. In practice tubes are used in lower temperatures until vapor phase LN2 (-150ºC to -196ºC). Micronic does not recommend to store tubes in liquid phase nitrogen (LN2), read here
. In practice tubes are only snap freezed in LN2 (without submerging the cap).