The leather area can snug up a bit, but generally do not shrink.
Really think through what you are buying and what the real purpose is. For CDI factor or zombie killing, anything will do. If you are using them in combat or around any explosive/flammable items, stick with kevlar or nomex.
Look closely at what Oakley, Mechanix, etc. are made of. Anywhere the rubber, plastic, spandex, nylon, velcro, etc. etc. touches your skin, is an area of flesh you will lose when you are exposed to high temperatures.
The burn injuries coming out of the sandbox are nasty. Losing fingers is pretty common in burns. Good gloves can prevent this, bad gloves will guarantee they are coming off.
Think about this with all your gear. Polypro neck gators and hoods are another common item that are available in kevlar or nomex. Think about what your polypro hood will melt to, or think about what your kevlar hood can protect.