I live in Florida and am concerned about sun exposure to my forehead and neck while biking. Has anyone seen a bicycle helmet with a wide brim all the way around?

A Google search suggest that they either don't exist, or are very rare. Mostly I saw home-built adaptations and suggestions to wear a hat under the helmet.
Maybe something like this would work: https://www.campmor.com/outdoor/gear/Product___63487

I was just going to suggest something like that too but honestly I think it would also cut down on his ventilation. Maybe he could buy the hat but cut out the center portion leaving only the front visor and rear flap. BTW: I found getting a helmet with a visor helped a good deal but sun screen on the tops of my cheeks; back of neck and thighs has been very important. You can probably jury rig a rear flap of some kind. Or just grow your hair long in the bacK!

I use some head sweats but maybe there is a headsweat that has a wide tail?

This is one of the reasons I wear a visor instead of a helmet. The air gets to my head, and the sun is kept off most of my face. In Phoenix, those two are a must.

https://img.alibaba.com/photo/11626871/Umbrella_Hat.jpg

Here is the sun helmet I made four years ago by modifying a Giro helmet:

https://www.bikeforums.net/showthread...&highlight=sun

Works great, better than anything else, and gets full ventilation. And has no downsides in terms of function or comfort.

For the most part, helmet manufacturers are not into building practical functionality into road and mtn bike helmets.

So ditto what someone else said about there being nothing on the market -- don't hold your breath.

Go ahead and make your own if you got the mad skilz! It can't be that hard -- mine only took about 50 hours of work, heh. :-)

I've attached stickable velcro dots like this:

https://img.diytrade.com/cdimg/874370...ircle_tape.jpg

to my helmet and sewed them to a piece of fabric that goes around the back. Eventually the dots around the helmet will fall off then I go to crazy glue. You don't need any fancy fabric. Basically, hold up some fabric to the sun (preferably dark). If the sun is peeking through the fibers, you shouldn't use it. Of course, if you have an old spf 50 LL bean shirt that you want to get rid of, you can use that.

As for the front, a helmet with a visor is best.

Also, I've weighed down the ends of the fabric with pebbles so it won't flap with the wind.

It's a little heavy, but very effective at reducing exposure to UV rays.

Peripheral vision is also a little iffy.

Like this guy in DC. I've seen him with my own eyes. Better rain protection than a helmet, too!

I've seen people wearing these kind of conical hats in Vietnam that might be of interest to you...

....

This contraption from Adventure Cycling

Living in Tucson, AZ we get a bit more sun than Florida . . . 360 days of it. 100+ degrees for 3 months and single digit humidity quite often.
Lived/cycled here for 31 years.
Wear a cycling cap and use sunscreen; so far so good.

??

Australia presents the same problems with sun exposure. I tried a helmet cover like the Adventure Cycling one above, but found it was uncomfortable and limited ventilation. I've had good results from Buff bandanas - good protection for the bald spot, reasonable protection for the back of the neck and cool when worn damp under the helmet: https://www.buff.es/en/index.php?p=USA. I've also used a Headsweats cap on a recent multi-day trip and liked it because of the visor and light weight. Australian link: https://www.deanwoods.com.au/store/prod2022.htm - pretty sure they're available in US.

Thanks for all of your inputs!

I have to admit I never would have considered the diver's helmet as a sun block option, but since I commute along a river part way, it might come in handy if I were to fall in. Just have to make sure that the air hose is long enough and does not get kinked. I am not sure about the umbrella hats though.

The Headliner Helmet Cover might work out. I also saw an instructables article which details how to adapt a brimmed hat to a bike helmet by cutting off the top off the hat to provide ventilation and cutting slats through the brim for the helmet straps. See htttp://www.instructables.com/id/A_DIY_Sun_Protective_Brim_for_a_Bicycle_Helmet.

Wow! That's the best I've seen, other than my own mod of course. ;-) Only downsides I can see to this re-mod is reflected UV still hitting you laterally thus still the need for sunscreen, however it will keep direct light off. Second downside is the brim flapping around and blocking vision in stiff headwinds and while downhilling at high speed etc.