This one-size-fits-all fit me perfect.  I assume I have a normal sized head.  I used the sandwich technique(latex over neoprene over latex) and in low-60 water temps I stayed warm.

Strap caused no chaffing or rubbing at all.

I did the Escape from Alcatraz triathlon on March 3rd 2013 with this cap. It kept my noggin nice and warm in the 51° San Francisco bay water. I used the sandwich method: normal swim cap / This neoprene cap / normal swim cap. Worked like a charm with no chaffing under the chin strap. Very happy with this purchase.

very small strap and head size. Not for adults.

Use for swimming laps. Good for warmth and does not come off. I wish it kept water out!

Neoprene, sneoprene all I know is that it works.  I was delighted from the very first swim with my new cap.  I was concerned that it might restrict my head movement in the water- but there was absolutely no problem.

I swim laps.  Need a close fitting cap to protect my ears. and head.  I tried another of your promising products, almost a helmet and it was too small.  I''m small, have a small head, wear small caps.  I could not get this otherwise impressive cap on.  It has velcro in two places.  I need that in a medium size.  I don''t see it offered in a larger size.