I have seen posts regarding taping the vents on a standard helmet to make it more aero and have some doubts about how effective it would be. But how about as a rain helmet? I got stuck in a downpour yesterday and it got me thinking. Has anyone tried it? I have a second Bell helmet that I tried taping last night with clear packing tape. Not an easy task. Has anyone actually raced like this? How can you quantify any beneficial aerodynamic effect? I will try it on my next rain ride.
Try this - Sugoi Stretch Bosui helmet cover:
http://www.sugoi.ca/prod.php?p=SUG99904U.002&k=59996
I can personally vouch for how well this thing works from having trained a commuted to/from work in Vancouver for many very wet rainy and cold winters. Also works well in the cold as it traps a large layer of warmer air inside your helmet.
Use those shower caps. They are waterproof, huge, and have an elastic cuff. When caught in rain or cold, I jump into Target, WM, or any drug store and grab a three pack for a few bucks. They go on and come off easy for weather changes during the ride and take up hardly any space in a pocket.

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I use swim caps on my atmos during the winter/springs day in NH and it keeps my head warmer. I should get free registration at Timberman for my free advertising.
I first heard about the idea of taping a helmet here on slowtwitch Tried it for a cold, wet race in Sept. Worked great, except now there’s glue residue on the helmet that I’m not sure how to get off without damageing the shell. I have an older helmet I taped up after the race that I’ll use all winter to help keep the wind out. I live in Ohio and ride outside most of the year as long as the roads are clear. Hasn’t been real cold yet, but it has helped so far.
Never really thought about the areodynamic advantages.
The path to enlightenment is fraught with pitfalls. If it rains, it just rains. The important thing is not to mind that it’s raining.
I have one helmet that is always taped. I did it first for the aerodynamics but kept the tape
on for weather issues. I found it really easy to do but mine has long straight vents. John Cobb claimed that the taped helmet was almost effective as an aero helmet. You may want to change tape as it gets kind of nasty with bugs, hair, etc.
My winter riding helmet has had vents taped shut with wide scotch tape to keep out the subzero wind! Maybe I should just ride with my LG Prologue…but that would really look lame riding to work sitting up in the wind, on a 15 year old MTB pushing all kinds of wind!
“I’m not sure how to get off without damageing the shell.”
Try ‘Goo Gone.’ It gets that stuff off.