Heat paks, by and large, are worthless when it comes to shipping plants. They don't last 3-4 days and even if they did, there is really no way to dissipate the heat throughout the box. Perhaps if someone used a special foil-lined box inside the shipping box, and several heat paks, that might work, but who does that? All my packaging has several labels that say either "DO NOT FREEZE OR REFRIGERATE" and/or "PERISHABLE". I also put large "DO NOT STACK" and/or "FRAGILE" labels. The postman and any other postal worker would have to be blind not to see my labels. Now, they might ignore them............
I also use plenty of newspaper, but never that glossy stuff. But when I am shipping this time of year, I simply don't ship if I think the temperature is low enough to harm my plants. That cut-off temperature is generally 40 F. I know I am very conservative but I just don't risk my plants to cold damage.
Lore Lisa, please tell me that those plants did not come from me!
