When equipped, its effects are an added +30 Radiation Resistance and +5 to the Medicine skill (up to a maximum of 100). The environment suit may be repaired using radiation suits and advanced radiation suits, though repairing it only affects the suit's damage resistance.
The environment suit may be obtained only by completing an optional objective during the Wasteland Survival Guide quest. While working on Chapter 2 of Moira's quest, she will ask you to reduce your health below 50%, and extends the task to optionally come back with a crippled limb. After completing this task and its optional objective, you will receive the environment suit along with some Med-X.
Apparently, according to game data, any NPC using the suit will receive 100+ radiation resistance, as the game checks if the user is anyone but the player.