The following is an exchange with a prospective customer who seems to be debating whether he wants to wear a cotton tallit katan or a wool tallit katan. Although I found some of his questions a bit surprising, I think the exchange may be instructive for some other people out there interested in buying a tallit katan.

With wool tallit katans, do I wear it against my skin? What is the general custom for wearing one? Thank you for your time.​

No, you can’t wear wool against your skin (try it and you’ll see what I mean). Even our Wool Comfort undershirt style tzitzit is not meant to be worn against your skin. You need an undershirt. It is made from a very soft wool, but it’s still itchy.

(I once told a customer who asked a very similar question that there’s no such thing as wool that can be worn against the skin. I was wrong. He was from New Zealand, which is one the the world’s leading producers of wool, and he gave me a quick lesson on Merino wool.)

People who don’t like to wear three layers choose a cotton undershirt style tzitzit garment.

How would I wash the wool undershirt tzitzit?

Personally I wash mine by hand, but I think woolite and a gentle cycle, cold water should be fine. The real problem is the tzitzit. Even on a gentle cycle they can get horribly tangled. Did you even buy one of these? If not, there are ways to improvise. You can tuck the tzitzit into a sock and tie it up tight and wrap rubber bands around it.

Thank you very much for the response. I know someone who wears the wool against his skin and he is an observant Jew. So I wasn’t sure if it was against halacha or not. Are there special undershirts for wool katan use? Or can just any cotton shirt work?

What if they made wool katans with a special thin soft lining that is only on the inside. The inside that touches the skin? But without commiting shatnez? It would be interesting. It beats 3 layers.

If I may ask, what is it that you wear? Do you wear wool katans?

I have both cotton and wool.

There are some opinions that wearing the garment against your skin (cotton or wool) is inappropriate. Not against halacha, strictly speaking, but sort of showing a lack of respect for a mitzvah item. But a tallit katan is in essence a regular garment, so it does not have the kedusha of items like a mezuzah or tefillin. According to that opinion, which is a stringency that not all poskim concur with, because a tallit katan is used specifically for the mitzvah of tzitzit, it’s more than just a regular garment. These opinions state that an undershirt is meant to absorb sweat, so creating a tzitzit garment that serves that function is disrespectful.

Shatnez is not an issue here because the fabrics involved here are wool and cotton. The prohibition is against a combination of wool and linen. Cotton and linen are not the same thing. Linen is made from flax/linseed.