You can read every last online review, but you really have no idea what a hotel room is going to be like until you arrive. And if you're the type who likes to travel with their own sheets and towels, you're probably also the type who would be interested in a portable pack-flat bath tub too. Carina Deuschl gives IKEA a run for its money with her XTEND bathtub that collapses to a mere 8.5mm thick. You could easily fit that into the bottom of your car's boot, or slide it into an especially large suitcase.
So how does the bathtub get so flat without the use of sorcery or some kind of alien technology? A piece of strong but lightweight carbon fibre was cut into an intricate accordion pattern using a high-pressure water jet. When extended, and supported with a set of included legs, the 7kg carbon fibre frame is strong enough to support not only a liner made from waterproof fabric, but a tub's worth of water too.
The XTEND tub also includes all of the basic plumbing you'll need to fill it, but that's a moot point because it doesn't appear as if Carina has any plans to put her collapsible tub into production. So the next time you're staying in a hotel, you're either going to have to risk using your room's tub, or just stick with a sponge bath until you get home.