What are "Stays" on shirts?
Stays hold the collar flat. They are permanent or removable from underneath the collar. If they are permanent, they are sewn into the collar. If they are removable they are flat and slide in and out of a slot under the collar. It is advisable to remove stays before dry-cleaning or laundering since most dry cleaners forget to remove them or replace them.

Why should I buy wool, cotton or linen as opposed to microfiber polyester or just polyester?
Wool, Cotton and Linen are "natural" fabrics. Natural fabrics allow the body to "breathe". This means that perspiration is not retained within your clothing leaving an odor. If your body can breathe, then odors are less likely to occur. Polyester, whether it is a microfiber or not is a synthetic (man-made) material that can trap body heat and perspiration.