Last Thursday, I went for a ride with a hoodie, jeans, leather gloves, and a fleece headband (ears) at a little under 40 degrees. Surprisingly effective, but while my ears stayed warm, my forehead was sweating. I have tried the wrap-around ear muffs for the back of the neck, but they don't want to stay on. I've also looked at a pair of ear muffs that go over the head, but they didn't fit under my helmet. A beanie would be a sweaty mess. Anyways, I am thinking about building something like this
into my regular helmet. Does anyone with more winter riding experience have any advice on the project?

The Bell Metro helmet used to have winter earflaps and vent fillers available as accessories. Unfortunately it's no longer sold. But you could make your own --

For the ear flaps, try Rox Dog Earz (https://www.bikeparts.com/search_resu...p?ID=BPC309496) or something similar.

For the rest, put a helmet cover over your regular helmet to block the vents. This will hold wamth in without making your head sweaty (at least, it works for me).

Like I said in another post, if you are going to be biking frequently in the winter why not just invest in a snowboard helmet... They are made to fight the cold and provide as much if not more protection than a bike helmet would.

Make sure what ever kind of helmet you use has some venting or it will be too hot for cycling. The bike free ride helmets are less expensive than snow boarding helmets and work great with goggles.

I use custom made ear canal phones which I made myself for about 15 bucks. You can buy the stuff to make them online. They are meant to be custom ear plugs for reducing noise. After I have made them I (very carefully) drill a hole in them from the outside down into the ear canal zone and insert a small tube. Then you can stick the end of your canal phones in the hole on the outside. Removing the normal foam plug of course. These are very comfortable, they seal well so you get better bass and they are warm as they keep cold air from going into your ear canal.

Here's a link to some cheap free ride helmets. Snow boarding helmets will have ear flaps or better ear coverage but will cost more. good luck.

https://www.pricepoint.com/detail/139...fle-Helmet.htm

Here is a bike free ride helmet with sound built in:

https://www.pricepoint.com/detail/170...und-Helmet.htm