Dressing up does no good as cyclists still sweat regardless of how cold it is. And eventually that sweat will saturate all layers of clothing and render their insulating capabilities ineffective. And in fact, there is even an extreme likelihood that once all layers are saturated, the sweat may in fact conduct the cold right to the body. And once that happens, you are in deep trouble! Being in that cold sweat, you may as well be staying in the water during a polar plunge for a prolonged length of time. And that is the absolute surest way to catch hypothermia!
Good science right there.