Edit 5/18/2020: I've created a new reusable version of this mask at https://3dprint.nih.gov/discover/3dpx-014379 -- the flat patterns have also been modified to fit the 5 head forms created by NIOSH. I will keep both of these submissions updated as the project progresses. 

The Basic Respirator https://basicrespirator.com is a disposable, lightweight and custom-fit respirator designed for emergency use. The mask is folded from a flat sheet of Tyvek™ or any other flat textile into a origami-like structure that's both rigid and flexes to conform to the curves of the face. A reusable 3D printed filter assembly inserts into an opening in the mask and accepts an N95 or similar filter. An aluminum nosepiece secures the top and a neoprene inner seal + gasket makes the mask airtight. It is very lightweight at less than an ounce (19.5g), uses 9.5g of filament and is cool and comfortable to wear. The same mask pattern can be sewn or folded from any textile without the need for 3D printing. A reusable version made from functional fabrics (such as ballistic nylon and electrostatic masterials) is under development.

Video of the wearer breathing deeply and opening the jaw while wearing the respirator. Because the mask is made from Tyvek, it flexes with the skin and does not introduce gaps.
Fit Test & Breathing 

Production, Shipping & Assembly
The filter assembly prints in less than an hour and doesn't require supports or cleanup. The flat patterns can be created by hand or with a laser cutter to both cut the outside shapes and pre-crease the fold lines. The mask is designed for flat shipping. It can be assembled in minutes onsite with peel and stick double-sided adhesive and adjusted for a custom fit. No sewing is required.
 
Custom-Fit
The flat patterns come in small, medium or large and can be customized for in-between sizes with additional strips of neoprene. When properly fitted, the respirator mask has a tighter seal than other disposable N95 respirators and appears to seal as well as a reusable respirator.
 
Breathing & Comfort
Breathing in the mask is comparable to a 3M reusable respirator (measuring perceived effort), but it is much lighter, cooler and doesn't cause sores. On the incoming breath, the seal is airtight and on the outgoing break, the mask ventilates under the chin. It fits under protective eyewear and doesn't cause fogging.

 
Filter Assembly
Video below shows how to insert the filter into the mask and locking it into place.
Changing The Filter

Testing

•  I've worn the respirator + an N95 filter for 2 hours consecutively and off/on all day. I can do strenuous activity without becoming lightheaded.

•  I can smell fragrant aerosols only very faintly while wearing it.

Adaptability & Materials

Fir healthcare workers, Tyvek™ 1073B was chosen as the best material for disposable wear because of its low cost, high BFE, breathability and ability to be sterilized, but the same pattern can be produced in any flat and flexible material including nonwovens or ballistic nylon for a reusable version of this respirator.

Adhesive-backed neoprene is used for the inner seal and gasket for the filter assembly. An antimicrobial option is available.  

Certain brands of adhesives can survive sterilization in an autoclave.

Model shown is for filter assembly only, a photos of the complete design with source files and assembly instructions are located in the "extras" section and at https://basicrespirator.com