The short answer: hang it, and use the dryer only if you know what the backing is made of. The published advice splits down the middle here, with several sources saying rubber-backed mats must never go in a dryer at any setting and several others giving twenty minutes on low as routine. Both camps are right, because rubber backing is a loose term covering natural latex, thermoplastic rubber and PVC dots, and only one of those genuinely tolerates warmth. The safe default is a towel bar with air on both sides, and the number that matters is that a thick mat takes 24 to 48 hours to air dry, which is why people reach for the dryer in the first place.
Disclosure: this post contains affiliate links, and as an Amazon Associate I earn from qualifying purchases. If you buy through them I may earn a small commission at no extra cost to you. I only recommend things I would use in my own home.