A refrigeration suit was a type of clothing used by the Breen, making up their equivalent of a military uniform. It was believed to be a type of environmental suit to keep a Breen's temperature at a lower level than its surroundings. The Breen theoretically wore them to maintain the cold temperatures on their home planet.
There were two distinct styles of refrigeration suits seen on Star Trek: Deep Space Nine.
The first was a standard uniform worn by regular Breen and Breen soldiers. As noted in the script of "Indiscretion", the Breen wore "armored pressure suits which protect them from Dozaria's harsh atmosphere."
The second was a more ornate version worn by Thots and other command officials. As noted in the script of "'Til Death Do Us Part", "We've never seen one of the Breen before – he has distinctive markings on his suit that we'll eventually learn identify him as a high-ranking general." This style had golden lining on the shoulders and arms, as well as distinctive gold stripes that ran down the center of the top of the helmet and down the top of the "snout" section of the helmet.