Every time I fly, I wear an undershirt and an outdoor padded vest.
Why? The interiors of most commercial aircraft are simply way too cold.
Until recently, you could adjust the individual air nozzle above your seat to try to limit, or completely shut off the air flow.
But on newer generation aircraft, like the Boeing 787 or the Airbus A350, those nozzles have disappeared, and when it comes to air flow and temperature, it’s apparently one speed and system fits all.
Also considering the dehydration effects inside the cabin, that’s just one more reason to dress in layers.
After all, it’s easier to remove a garment in flight if you’re too warm, than to freeze and not have anything warm to wear in the first place.