So, caveat: I think the guys in thi sthread trying to put ideals of a no-car society over the reality of what it's like to be poor and commuting every day on bike are full of shit. That said, I have spent most of 20 years biking to work in the vicinity of a big city.

In winter, you have to dress like you're prepared to be lost outside overnight with no shelter. Like, you have to learn to ACTUALLY dress for the cold, for extended periods of time. (And you have to pay attention to the weather report--if it's going to be wet, you need something that can handle being wet.) Most kids who try to bike to school try to do it in the clothing that they'd wear to drive to school. They either do not physically own the winter layers they need to stay warm, or they were never taught to properly layer.

But basically, you need probably 3 layers minimum in Chicago-type weather. Probably more if you're further north. I would regularly wear jeans with two layers of some type of pants underneath, like fleece and some other base layer, and on top I'd have long-sleeve shirt, t-shirt, another long-sleeve shirt or sweatshirt or sweater, and over all of that a heavy duty winter jacket. For my head I'd have a full-face mask with a thick warm hat on top. Sometimes a scarf too. For my hands, I'd have multiple layers, and I'd usually wear mittens rather than gloves because mittens are warmer, and I'd have more than one pair of mittens. When biking, at least one layer of mittens needs to be wind-breakery because that wind is COLD. For shoes, I'd have wool socks, sometimes two pairs, and real heavy-duty winter boots on (not sneakers or whatever).

The thing is, a lot of people who never have had to actually spend significant time out doors won't even OWN sufficient layers to stay truly warm in the cold. Either due to poverty (it costs money to buy really, truly warm clothes of the right material), or lack of knowledge of how to dress for the cold. (I lacked both when I was young!) Or they'll have thin cotton fast fashion when they actually need wool or synthetic warm-weather gear. Or they'll be concerned about looking stupid (because if you dress properly, you look dumpy and not cool.)