The size medium is extremely small, might be good for a young child with a smaller head as this is certainly very small. Got the large size and it is still much smaller than the Tyr racing cap, but fits a teenager with medium size head.

I bought this cap for Olympic Trials in several weeks... i am a 16 year old guy.  I have a medium sized head (so i thought), but this "medium" sized cap is made for 8 year olds.  it is TINY.  There was no part of my ear that could even get under the cap.  I looked like dumbo!!!!!

I use it for competition and if feels way better than any other cap that i have ever tried. I first bought the Speedo AquaV but it was to big, and a air pocket formed on the top. This cap is completly diferent it is a lot smaller, but more stretchable and it has a uniq cut down the neck top get a good grip and stop it from forming air pockets. All i all this is a great product, that feels a bit to small a the begining but it streches out in a few weeks. So if you want a great competition cap that holdes you're goggles tight this is you're best buy even known it is a bit expensive.

I use it for competition and if feels way better than any other cap that i have ever tried. I first bought the Speedo AquaV but it was to big, and a air pocket formed on the top. This cap is completly diferent it is a lot smaller, but more stretchable and it has a uniq cut down the neck top get a good grip and stop it from forming air pockets. All i all this is a great product, that feels a bit to small a the begining but it streches out in a few weeks. So if you want a great competition cap that holdes you're goggles tight this is you're best buy even known it is a bit expensive.