this is a cheap-and-cheerful 'just in case' helmet cover that folds up small to stash in your bag. It's got a drawstring, which is nice for quick installation. I'm a daily rider and if i'm leaving the house in the rain, I will use the much heavier Sugoi Zap cover (link at the bottom). This is permanently installed on an old helmet so I don't have to fuss with it on rainy mornings. It's also legitimately waterproof and more breathable with awesome reflectors...but who wants to spend $25 on the extra cover for the saddlebags which almost never gets used (I actually have three, so I can dry one set, have one set to wear if it's raining, and one set already packed up in a saddlebag if it's forecast to rain)
If you're an occasional rider, this will probably be fine for the occasional rain. If you're a daily rider, spring for something better, but I would still want a back-up.
Sugoi Zap 2.0 Helmet Cover, Black, Large

A bit disappointed with this purchase and kind of afraid to use it. This product slips over your helmet and has a draw string to tighten it around your helmet's rim. So far it doesn't seem very snug or that it would stay in place in a downpour or strong wind. I love the color and the reflecting designs on it, but I'm almost afraid to use it. I will update my review once I use it in the rain.

My design suggestion would be to use something more elastic in the draw string so that you could cinch it up better and it would grip.

Used it twice an the silver reflector stripes are coming off. Poorly made

PROS:
I picked this helmet cover up a little over a year ago and it has served it's purpose admirably during that time. Between the bright flourescent coloring and the reflective striping, it provides great visibility to vehicles. It works well as both a windblock (the primary reason I ordered it) and to block the rain. As a bike commuter, I was looking to cut the chill from the wind and this works wonderfully in that case.

CONS:
As others have mentioned in their reviews, the sizing doesn't seem ideal but I'm able to make it work over my helmet - it tightens down via the string just at the bottom edge of my helmet but doesn't fully wrap around the bottom. Due to this fit, it can slide a bit but has never been an issue for me.

The drawsting works okay, but would work better if it were just slightly bigger in order to cinch under the helmet. The drawstring was a source of consternation in the last few days as the drawstring had pulled itself out of the threading/seam. I was able to thread the drawstring back through and tie it together to make the cover functional again.

Overall, the helmet serves it's purpose at the price point and is able to overcome it's flaws.

I purchased a few of these. One for my young (10 year old) son who likes to bike everywhere all the time, and one for my much more conservative teenage daughter (who also likes to bike but in more of an adult way). My son actually commented on how he liked how reflective it was. My daughter liked how it helped with keeping rain out of the helmet.

They have very different shaped helmets (my son has more of a "ski - or round shaped" one) my daughter more of a "normal" bike shaped one - but the drawstring and shape of the fabric worked for both.

I like feeling they're safer with the reflection from car headlights.