I have an Arai helmet and ride through the winter. It can get chilly in New Jersey in January and if you don't like icicles being stabbed in your face, you need to fix your helmet.
First, cover all the vents with some sort of tape. Electrical tape or clear wrapping tape can be used.
Second, use the fuzzy part of Velcro to line the perimeter of the face shield (attach the Velcro to the helmet, not the visor). When you close the visor, there should be a snug fit all around the visor.
Third, make a "chin-flap" to keep wind off the neck and to reduce noise. I used an apple-warmer for some time but found it cumbersome and they restrict head movement. So, I hacked it to bits and came up with a short chin-flap which extends from ear-to-ear and extends about three inches below the chin-bar on the helmet. This is very effective. Use Velcro again to affix the chin-flap to the inside of the lid.
Fourth, now that the helmet is sealed you desperately need a Fog-City visor thing. These stick on to the inside of the visor and prevent fogging. They work.
Fifth, to get a really tight fit on the face shield against the Velcro, you can undo the screws which hold the visor to the helmet, then push the visor against the helmet and tighten the screws whilst pushing the visor onto the helmet.
Sixth, There must be some sort of product liability reason for the utterly ludicrous black blob on Arai visors which is intended to be used to open the visor. Try opening the visor with a winter glove with your right hand and you know what I mean. I drilled a small hole in the center of the visor at the base and installed a small nut and bolt to form a visor opener which can be used with either hand and provides ample grip. The screw sticks out about 3/4 of an inch. I used the sort of screws which are attached to computer cables to hold them in place. Be aware that making this modification will cause your warranty to be voided, your sex life to terminate, your hair to fall out, etc.
Done properly, the above will completely eliminate draughts and a much quieter ride than before - use earplugs and its like being in the back of Rolls well, almost.
Finally, having effectively sealed your helmet, there is a good chance that you will suffocate.
Tony Dilworth - Nov 20th, 1998