This is a revision to the medium size of the excellent mask created by Chris Richburg and team (found here https://3dprint.nih.gov/discover/3dpx-013429). I have revised it to allow printing on hobby style FDM printers (PLA, PET-g etc). The revision moved the filter cover to the interior. Reduced the overhang of the area that contacts the face. This can be printed WITHOUT supports and uses the cover on Chris' post. All caveats listed on Chris' page apply. This version has been through no clinical testing and I can not vouch for it's ability to be sterilized. Produce and use at your own risk.