Having never laid my hands on one, I'm not certain, but I think they're based off the same material as judo uniforms are. They look similar to my untrained eye.
The Revival Clothing ones are not. They're a single layer heavy cotton canvas or cotton duck.
Unless if you're thinking of the Jess Finley ones, which are made of monk's cloth, and that is very similar to a Judo gi (though a little lighter):
