When I was using cotton I would take it out of the coil and take it apart to see that it was black all the way through to the center but with the hemp I remove the wick and its black on the outside but the middle is still nice. I found hemp twine, cord in stores but had reservations about buying it since it felt waxy even though it said on the package 100% hemp. I got my hemp fiber in a ECF coop many months ago and wish it would be coop'd again so I can get more since I've shelved all my silica, ekowool and cotton and just use the hemp fiber.
After using a particular wicking material for a while you get a feel for it and I can feel in the vape if the wicking material is beginning to loose performance. I could never figure out how some can go weeks with a particular head or build before changing...how bad does it have to taste before some change their material.
Another thing I did but still isn't as good as hemp is to unbraid ekowool into single strands and with the bead threader again insert several strands into my builds, it gave me the easy like hemp to insert into the build, some dryburn ability but it doesn't wick as good as the hemp so that fad didn't last long at all.