The fogging problem can be solved. My sons, first used Smith Knowledge Fan Goggles with this helmet. Fogging problems went away until last year. We then ski in Japan and the fogging returned. They now use Swan Fan Goggles with their Smith Troy Lee Helmets (XXL) even with their glasses on. They have no more fogging problem at all! (This was tested after two trips in both Dec. 2010, and Feb. 2011 skiing in Japan, under extreme high wind and about -15C mingled with heavy snowing). Location - Rusutsu and Neisko. p.s. They both are double diamonds at now 10 & 12. p.p.s. You can see my son's photo above. The one with glasses and with the helmet I posted before (under Ant2787945 above).

My son is 8 and has 51 to 52 cm head size. He found Large size of this helmet is better for him. My other son, who is 11 and has 55 cm, found Large size is too small for him. He ended up using D2 XXL here. I tried both sizes, and can only accept XXL size. My head is about 56 - 57 cm.
Note that those using glasses, the Knowledge Turbo Fan will be partially (mostly) blocked on top fan outlet. XXL size is better for the fan outlet. Must use Black color because the lining is different in other color even if they are all Knowledge Turbo Fan.

Both of my sons wear glasses. They both ended up using XXL with padding included. But in that case, BLACK Knowledge Turbo Fan can now squeeze for the XXL size helmet (not for Large size D2 helmet).

Not totally true. If we use the Turbo Fan Goggles from Smith, and put on the Helmet, the fan outlet is partially blocked by the Helmet.

Knowledge will fit over your glasses and works great, as previously mentioned.

Agree! Used the lens without fan and failed badly. Fan is a must and Smith is the best I have seen. Looked at others with fan but Smith seems the best so far. If others find something better, please come here and let me know too. Thanks!

Knowledge will work with glasses. My son is far sighted 1,000 and now have clear vision using the Knowledge Turbo Fan!!!
p.s. The Knowledge will work for me, an adult as well with a much bigger face. Nonetheless, Knowledge does not work for my younger son, 9 year-old boy with a small face.