New England Biolabs ships its products in plastic foam (polystyrene) containers with gel ice packs and recommends that its distributors do the same. Gel ice packs are kept at -20°C for at least 72 hours prior to shipment and the polystyrene boxes are tightly sealed. Tests have shown that products shipped under these conditions will stay at 2°C to 8°C for more than 24 hours. Testing at NEB has shown that there is no difference in activity and stability between enzymes that are shipped with gel ice packs and enzymes shipped on dry ice.
While New England Biolabs recommends storage of its enzymes at -20°C, exposure to higher temperatures (4 to 10°C) during shipping does not pose any risk to the enzymes. In fact, during the purification process (up to 3 weeks) enzymes are maintained at these temperatures as they are purified away from proteases and other contaminants which might interfere with their stability. Furthermore, each enzyme is shipped in a specific storage buffer which has been optimized for long-term stability.
NEB enzymes are stored in buffered 50% glycerol and remain liquid at temperatures down to -35°C. If these enzymes are shipped at colder temperatures (for example, in the presence of dry ice) the products will freeze. Proteins subjected to repeated freeze/thaw cycles may lose activity.
We have used these shipping conditions for the 40+ years that we have been providing DNA restriction and modifying enzymes and related products to the scientific community. If this shipping procedure posed any risk to our products, we would change the procedure immediately.