it's gotten to the point now where laptop manufacturers tell you not to put sleeping/hibernating laptop into a bag at all due to amount of heat they still generate even while sleeping [0]. Only those that are fully shut down should be placed in a bag (according to them).
[0] https://www.dell.com/community/XPS/FAQ-Modern-Standby/td-p/7...
Previous HN discussion: https://news.ycombinator.com/item?id=28639952