I wondered this too! Thought it was bumps-up for the slipping reason, but then tried it bumps down and like it better. It feels squishier that way, and is still plenty sticky. I would try both ways and see what you think.
I'm glad you mentioned that about the chemical smell. I bought mine at a regular store not too long ago (previously just used the carpet, which wasn't as good at all). I didn't ask any questions about it, and just grabbed one. It does have a smell! Hopefully it will fade out soon. It only bothers me when I have to lay face down on it.
