Normal Breen body temperature is 235 Kelvin; exposure to temperatures above 260 Kelvin will kill a Breen within minutes. Given that most known major space faring species live on class M planets with an average temperature far above that of Breen, the Breen have had to develop environmental suits of great capability and reliability in order to co-exist with others. Given their nature, it is understandable that the Breen have become one of the Alpha Quadrants leading experts at creating and maintaining extremely cold environments. They are acknowledged experts on cold storage of chemical compounds.

Given the environmental difficulties, casual visits to Breen worlds by non-Breen are virtually impossible. The Breen strongly discourage visitors, and all those who do visit Breen worlds are confined to purpose designed encampments. Combined with the fact that the Breen habitually design environmental suits which hide their faces from view, this has given them their air of mystery. This has been further enhanced by the fact that some empathic species, most notably Betazoids, are unable to detect the thoughts or emotions of the Breen. Much of Breen is known to be a frozen wasteland, and it is widely thought that the Breen have deliberately avoided large surface developments for cultural reasons.

Nevertheless, much has been discovered about the Breen over the years. They have developed organic technology to the point where they routinely use biological spacecraft. Some of these are fitted with cloaking devices, a technology the Breen apparently invented independently of the Romulans and Klingons. They use disruptor type weaponry rather than the phaser technology used by the Federation.

The Breen have something of an aggressive history; Breen privateers have conducted raids against other species on several occasions. In 2366 the Breen attacked and captured the Cardassian vessel Ravinok, using its crew as slave labour in the Dilithium mines on Dozaria. In 2372 the Breen also attacked the Bajoran colony of Free Haven and the reputation of this curious species has been summed up by the Romulan saying "Never turn your back on a Breen".

In 2375 the Breen moved from a policy of low level hostility toward the other major powers to one of open warfare when they allied themselves to the Dominion. As well as their conventional forces they brought to the alliance a unique weapon - a form of energy damping system which could completely drain all the main power systems of a Starship. The weapon proved decisive in the second battle of Chin'Toka, allowing the Dominion to retake the system after inflicting huge losses on the Allies. Fortunately the Allies were subsequently able to capture an example of the Breen weapon along with the technicians who installed it, allowing them to develop countermeasures.

The Breen continued to fight with the Dominion until the end. In some respects this actually worked to the Allies benefits - the Dominions increasing reliance on the Breen made the Cardassians feel more and more isolated and abandoned and was a contributory factor in their eventual split from the Dominion. When the Dominion surrendered the Breen were left with little choice but to do likewise rather than face the prospect of open warfare with the Federation, Klingon, Romulan and Cardassian forces simultaneously.