The term "cotton tzitzit" can be confusing because generally in use it means a cotton tallit katan garment with wool tzitzit strings tied on. But sometimes when people say 'cotton tzitzit' they really mean what they say! Here's a question regarding the latter, which we received yesterday.

Do you sell, or know anyone who sells, heavy-duty cotton tzitzit strings (to put on a cotton poncho)? I've two reasons for asking:
(1) The Opinion of the Alter Rebbe (Lubavitch) - it is preferable (though not mandatory) to use cotton tzitzit on a cotton garment.
(2) Tza'ar Ba'alei Chayim - Sheep are brutally mistreated in the commercial wool industry (as you can easily verify via Google) and thus I personally avoid purchasing wool products, just as I avoid leather.
Alternatively, even if not made for tzitzis per se, could I use heavy-duty cotton string that I cut myself (or would they unravel in a second?). Thank you, Michael L. 

I explained to Michael that it's not just Lubavitch that holds like that. The Mishnah Berurah states the exact same opinion. 

It's a bit surprising that with so many tzitzit string manufacturers out there, none is making kosher cotton tzitzis strings. We've gotten this request a few times in the past. We've also received requests for a cotton tallis, and I've heard there are manufacturers slated to introduce very nice cotton tallitot.

If you look up cotton tzitzis online you'll be very frustrated, because usually when people use the term "cotton tzitzit" they mean a tallit katan garment made of cotton (with wool tzitzit).

I suggested a possible solution for Michael -- but it would be quite expensive. There is a famous tzitzis string maker out there named Valles (וואלעס) who has been making super kosher tzitzis strings for decades. He has all sorts of stringencies above and beyond the kosher standards most people hold by. I remember reading once that he uses special herds and goes out himself to the herds to select the right sheep. I have a feeling his sheep conditions might be different, and he would almost certainly have first-hand knowledge about sheep conditions.  

The only problem is that I think Michael will have to do all his research in Hebrew or Yiddish.

In any case, I urged him to drop his idea for heavy-duty cotton string. I don't know whether it would hold up or not, but it's 100% non-kosher for tzitzis strings. Tzitzit must be made with the intent to fulfill the mitzvah of tzitzis. At what stage does that start? When you start tying? Earlier, when you start twining? Even earlier? To understand the issue, refer to this blog post. According to Rabbi Valles, it starts even before the Niputz stage.