It's quilted fabric - it doesn't contain any liquid, but it absorbs and holds a lot of water when you soak it.
How long it stays cool depends on a lot of things - how soaked it is (more soaked lasts longer, but gets your shirt wet), how cold it is when you start (more than a couple hours in the fridge doesn't change anything, and more than 30 minutes in the freezer and you can't unfold it! :P)
And then there's temperature, humidity, and airflow. It relies on evaporation, so it probably works better in Phoenix than Miami. It needs airflow, so my highway ride works...unless there's a traffic jam then it's like being in a sauna! And the the hotter it is outside, the quicker it loses its cool and dries out.
Which is to say, it's better than nothing, but it's not magic. Keeping your "core" cool helps, but the rest of you is still pretty hot
Really, the question isn't one of how well it works, but about your sanity:
"It's 97 degrees - I think I'll put on a second layer of clothes, boots, gloves and a helmet....and sit on an engine!"
I know where I stand!
Ride safe and stay cool!
Rob in KC, 2014 Versys 650, 18K miles