thanks for the help guys. as for the helmet, its a giro shiv. best helmet ive ever owned btw.
with the shiv i always leave a small gap above the goggles so i have some ventilation. i think its more an issue of my face getting hot, which i thought the anti fog treatment would still cope with. turns out it cant.
when i wear my face mask i tuck it under the goggles. that forms a seal which means my breath can only go down, and not up into the vents. that helps a lot, but if im hiking a feature and my face gets hot the lens fogs up like a bitch. id love to be able to fix that..