Great addition to your 40mm gas mask if you have breathing problems or just want to save energy for more important things, like surviving. It is made of hard plastic and seems durable enough if taken care of. Pumps sufficient amount of air to take the strain of breathing through a mask and also causes positive air pressure to keep out what you do not want to breath in. It is a little expensive, but better than having a cheap alternative that does not do the job. Read more