I have developed an itchy rash under my watch band. I am wondering if anyone knows what the band is made of? Has anyone found a band that resolves this issue?

I had the same issue, switched to a mesh metal band, no more rash. 

Thanks I’m glad metalmesh is a good option 

That’s good advice thanks. I do think a looser band gives more air flow. I now switched to the opposite wrist.

Exactly same issue just few days after purchase. Such a disappointment!

Jarrad and Mortefer have given you the most common reason for the rash under the band. No matter what type of band you use... Obviously if the skin can breathe it will always be better..

You need to keep it clean from soap, dirt and dry from sweat. 

1. The mesh band I use is made by Meliya. I wear it 24/7, reasonably snug so I get good HR info. No rash like I got with the silicone band. 

Mesh is a good option as it provides better ventilation than a solid band like the silicone one.  Here's a link for the Meliya one that fits the 3S:  www.amazon.com/.../B0DQNZWFM6