I initially ordered this, but the product didn't fit in the sleeping bag very well, so I changed it to one size smaller. It's been a great purchase.
Verified buyer

Exped Air Pillow L is a bit asymmetric inflating trekking pillow, which provides comfortable head support while sleeping on hikes. The packing size is very small and light pillow travel easily with you. This L size is 14 cm wider, 7 cm longer and 2 cm thicker than size M.
One of the product videos shows how the size M pillow fits into a sleeping bag hood. This L size does not fit, and is meant to be used under your sleeping bag.