Who are you tie-ing up in the bath tub? And, why?
Hemp
I’m picturing Tommy Chong ripping off the robe’s pocket and rolling it up.
(Yes, I know about hemp as a fiber, etc)
The new bamboo fabric is nice and sustainable.
You shouldn’t smoke it though.
Assuming the OP meant bathrobe, terrycloth is the best bet for absorbency. It comes in different thicknesses. I have a VERY thick one for winter and a much lighter one for warmer weather.
I have a thick terrycloth bathrobe that I never use, except sometimes in the winter, if it’s cold enough. Then I’ll add it to the foot end of my bed to keep my tootsies warm.
It occurs to me that the belt of this bathrobe is pretty long. In a pinch, it could be used as a short rope. A bathrope, as it were. For the record, it is also made of terrycloth. Does that help?
Now I’m wondering for what other purposes one would wear a bathrobe…
Howdy! Welcome to the Dope. (I hope it’s been good things…?)
Hey! Don’t just think you can hijack this highly focused discussion of bathropes, bat-ropes and bathrapes.
I guess you haven’t seen the pictures from the last mod loop gathering.
Google Cotton,waffle weave, robes. They work well instead of a towel. they are thinner than terry so cooler and dry quicker.
Hotels use them so they can be had crazy cheap if you are willing to wait for shipping.
Good luck!
Cotton. My current one which I happen to be wearing is over 10 (possibly 15 now) years old and good summer or winter.
It also happens to be black and has the Klingon Imperial Crest on it.
I bought two; one for me and one for a friend when she was appointed as a judge in the county courts.
PS – I mostly opened this thread because I figured anything that started out with bathropes would make good reading.
I like fleece. But for me the point of the bathrobe is to keep me warm, whether or not I just got out of the bath. So if it was too hot, I would just take it off.
Whatever it is, it absolutely has to be non-static. So cotton is good.
What about pampoo?
ISWYDT 
BTW, OP, on a ship you don’t refer to them as bathropes, they are called “Bathsheets”. Thank you.
The best bathropes are stolen from AirBnBs in Germany.
Bondage in the shower can be pretty sexy. But yeah, you want to use a lightweight bathrope that doesn’t absorb too much water and get real heavy - distracts too much from the fun. 
The bathrobe is dead and Harvey Weinstein killed it.
It was to give to new next boyfriend. Duh.
Her new boyfriend. That’s what happens when you change your in in mid-sentence.
How do you change your ‘in’? Does it require surgery? 