most heat packs are air activated. it needs air in order to produce heat.
what i do with my packaging is i put more or larger holes when the weather is colder. i also place the heat pack on the side of the box centered on an air hole. usually this hole is the largest hole appx. a qtr inch diameter. i have no choice in shipping in cold weather as i ship from buffalo area.
last week i sent some snakes out and it was quite cold. they arrived safe and sound.
if you would like i could try and contact the buyer to find out if he remembers the heat pack still being warm or cold.
i use the 18 hour hot hands from walmart.
adam jeffery