From the pattern notes:

“I used some Rowan 4 ply cotton I had on hand, but a much better yarn would be be an unbleached 4 ply Hemp. Some sources I know of are http://www.houseofhemp.co.uk/acatalog/Natural.html which is 100% hemp yarn and http://www.lanaknits.com/usahempton.html which is a 50% cotton 50% hemp mix. House of Hemp are based in the UK and Lanaknits are based in Canada but both sell worldwide.

Using hemp would make the tampons ultimately compostable and the hemp plant is very good for the ground it’s grown in. The yarn when you buy it is often crisp and coarse feeling, but once washed it becomes much softer and more comfortable on the skin, which is fairly important for this pattern

If you’d prefer cotton or are having difficulty finding hemp, them please use an unbleached 4 ply cotton yarn.“