In the sun, mine have started to get soft and stick together. When they cool back down, you can roll them between your fingers to break them apart again. A co-worker of mine was testing a sachet for me of a scent that I don't particularly like. She left it on her dash board one day (all day) and it turned into a solid mass of goo and seeped out of the organza bag. I think that if you leave them in the car either hanging somewhere like the rearview mirror or in the shade, you should be fine.