I recently bought a pair of Adidas cycling bib knickers (made in 2006, new with tags). I knew this model came with a shorter-than-usual pad as per customer reviews, but they are really comfortable, and they are Adidas (a brand I'm a fan of).

What I would like to do is add a larger modesty patch at the front. I'm planning to cut the patch myself (trying different shapes and sizes first), and then take it to a seamstres to stitch it to the knickers.

I'm looking for suggestions as to what type of fabric would be good. I though of the chamois used for car detailing, but I'm not sure that would have any chemicals that should not be in contact with your privates. The fabric should be soft and smooth, rigid enough to contain your boys properly, but not too rigid that it would bulge up and rub against your skin when you are in a sitting position.

Any suggestions will be appreciated.