Would anyone have any suggestions for sizing?
I normally wear a size Small in Iron Heart work shirts and a size Small in Iron Heart sweatshirt hoodies.
Looking for a good layering vest and have been looking at size Medium for layering based off of measurements.
Is it a good general rule of thumb to go up 1 size for layering in these vests?
I prefer to wear them closed than open.

I own the 14oz Type 3 jacket in a size Small (36) and am only able to wear it with a t shirt, How would this vest differ from that?
Thanks.