I bought Bell Segment helmets for my whole family. Being the more accident-prone of us I was the first to demonstrate its quality when I was hit by a car. It was too fast for me to register what happened but the witnesses stated I was flipped over the car and landed head first on the back of my head before rolling to a stop. I do remember the impact of my head on the ground and thinking to myself "Well, this is going to be bad". My helmet is ruined (the inner foam liner is very broken) but I am not. I definitely recommend this helmet

I'm used to the hard-shell type of Bell helmets. This new style has a flexable outer shell that I don't like. The inside liner ,that was across my far head ,had a rough bottom edge that was annoying. If I tried to move it , it looked like the Velcro buttons , that were glued to the inside of the shell , might rip off . So I left it alone. I'm not saying that the hehmet won't work, I just don't like it for those reasons . I will go back into a bicycle store that sells Bell , find the type that I like , and try again on Amazon for that model.

The small size seems OK. My 12 year old measured 21.5 inches, which is right at the limit for this size (21.6 inches max). It fits snug with the smallest pads in it. Biggest problem is getting him to wear it forward to protect his forehead, he likes to push it back too much.

He will need a medium soon, but I'm glad I got this size for now, rather than one that is too big so he can "grow into it." I will not complain about spending another $30 in six months to protect my kid's skull.

I bought a Medium according to the size guide and it fit great. I made the fit even better/ tighter by swapping one of the padding strips that came in the package for one of the thicker ones. Make sure to try different padding levels to adjust the fit of the helmet (it should be snug!)

It does make my hair a bit sweaty on warmer days, but that doesn't bother me too much. If you sweat very heavily you may wanna consider a helmet with more vents, but for my purposes this helmet is perfect. Plus the color matches my bike, love it!

UPDATED REVIEW: I give it FIVE stars now!

Size Medium was TOO SMALL!! I measured my noggin at 22 inches at the largest part. The sizing chart called for a medium but I'm returning it for a large. Update: large is in, fits perfect with larger inserts - Kryptonite color can be seen from SPACE, looks great with the matching Specialized bike (sold separately).
NOTE: the Matte Grey/Green is a Matte grey HELMET with a Green chinstrap. Video review attached of what it looks like in REAL LIFE in direct sunlight - feels like it would protect from a decent spill, many of which I intend on having ... but off road only!