a month or so ago i received a shipment of small croceas and the box only had one heat pack and it was right next to one of the bags, so i can only imagine what the first hour or two must have been like for the clams, then when it arrived the next day of course it was the same temp as the outside air- about 50 degrees! i was not very happy, but the clams were still alive. this isnt the way to do it but if something happens they still have a chance for survival. IMO the right way is to have two or three hand warmers on top of some bubble wrap or styrofoam then a layer of bubble wrap then the clams all double bagged then a layer of bubble wrap then two or three hand warmers then another layer of bubble wrap. i use a cooler instead of a box which will eliminate the need for the first and last layers and if you have extra room inside add jugs of tank water to help maintain the temp.