I have been using the Activa mask for years and it is the best one I have found. I have to use a fairly high pressure and it seals beautifully. One trick is to not get the straps too tight. When you turn your machine on, the bellows will inflate and give you a good seal. It is also important to get the right size. I found a large mask, which I previously used, leaked and caused skin issues. When I went to a medium, problems went away, seal improved and I have been a happy sleeper ever since. It is important to replace the cushion periodically as it will lose its seal if it gets too old.