The compatible gas cartridge for the Horse Pilot Airbag Safety Vest is flat and curved for comfort and discretion. Four independent gas cartridges each inflate a specific part of the vest, resulting in the fastest inflation time on the market. All Horse Pilot products come with a 2 year warranty. Important: You must replace the cartridge after each successful inflation! If the airbag does not inflate it is almost always because the cartridge was not installed correctly. Instructions on how to replace the cartridge can be found in the user manual provided with each vest, as well as attached to each gas cartridge. If you need further help please see this video. Do not hesitate to call or email us if you have more questions. Horse Pilot Airbag Vest Refill Gas Cartridge