I've recently bought a TON of skull caps from different brands, trying to find something I can fit under my motorcycle helmet without making the helmet no longer fit correctly.  Everything I tried had stitching that simply made the helmet no longer fit "right". I found an underarmour mesh skull cap that I like, but it's actually a bit to tall. meaning I have some slack at the ears.

This product; however, fits perfectly all the way around.  Fits my 24" head and goes to JUST behind my upper ear lobes.  Fits perfectly under my 1/2 helmet, and now wish I could find the receipt to return the UA (as I've already returned the rest)