The Thunder Tactical Shooters club has alternatively switched between "concealment on" and "concealment off" depending on the time of the year. Obviously when it is hot and humid outside (Summertime) we would like to have a club-wide standard of "concealment off." But ... we have recently been made aware of a rule change at IDPA headquarters that prohibits us from doing that any more.
Rule 188.8.131.52.states "IDPA is a shooting based sport based on concealed carry. All courses of fire will be shot using a concealment garment unless stipulated otherwise."
What this means is that you should plan to bring your concealment garment (shooting vest) with you to all IDPA matches. If the Match Director stipulates that a single course of fire - or multiple courses of fire - do not require the garment then you will NOT need to use it to shoot the course. Don't rely on that happening for many stages though, regardless of the time of the year.