This fleece vest is something that's come across from trading floors.
It started at SAC capital management (now Point 72). SAC was famous for very carefully creating an environment for peak efficiency. Noise was bad for concentration, so the SAC trading floor was really quiet. Even the phone ringers were off. You had to pick up the phone when the light blinked. They found that people tended to perform best when the thermostat was set to quite cold, so that's what they did. Then they found that you didn't have to completely freeze but but being just a little cold put your brain in the right state so vests became popular. You were't uncomfortable but your arms were cold so you got the performance benefit for the least amount of discomfort.
Making a trading floor really cold is actually quite a convenient thing to do because other than a data center there aren't a lot of places with a higher density of heat generating computing equipment than a trading floor and also because traditionally people wore suits so a little cold was fine.
The Jeans, shirt and fleece is not or at least post the initial spread from SAC was not a Wall Street thing in general. It was quite specifically a trader's "uniform". You didn't want to wear your suit jacket all day long because the mesh on your office chair (usually an aeron) would rub against it and make holes in the back of your jacket. So you took off your suit jacket, took your vest off the hangar in your office, hung your jacket and put on the vest if it was cold.
It started at SAC capital management (now Point 72). SAC was famous for very carefully creating an environment for peak efficiency. Noise was bad for concentration, so the SAC trading floor was really quiet. Even the phone ringers were off. You had to pick up the phone when the light blinked. They found that people tended to perform best when the thermostat was set to quite cold, so that's what they did. Then they found that you didn't have to completely freeze but but being just a little cold put your brain in the right state so vests became popular. You were't uncomfortable but your arms were cold so you got the performance benefit for the least amount of discomfort.
Making a trading floor really cold is actually quite a convenient thing to do because other than a data center there aren't a lot of places with a higher density of heat generating computing equipment than a trading floor and also because traditionally people wore suits so a little cold was fine.
The Jeans, shirt and fleece is not or at least post the initial spread from SAC was not a Wall Street thing in general. It was quite specifically a trader's "uniform". You didn't want to wear your suit jacket all day long because the mesh on your office chair (usually an aeron) would rub against it and make holes in the back of your jacket. So you took off your suit jacket, took your vest off the hangar in your office, hung your jacket and put on the vest if it was cold.