This is a homemade particle mask as made by Tina Seaton.  It is pretty simple, and works very well.  The "pipe cleaner" used as a stiffener is something that makes this mask work very well by allowing you to form the mask around the nose.  Apparently the large diameter pipe cleaners cut in half work out very well. Dimensions can be adjusted to better fit smaller or larger people. there are many other designs available on the internet.
 
Several studies have been done on the best cloth to use.  Tea towels or dish towels appear to provide the best filtration, with two layers providing up to 97% filtration, but being almost impossible to breathe through.  The flannel here works very well, and is normally fairly comfortable. Normally, new cloth is washed prior to making the masks. then washed again afterwards. Using soap and as hot water as is available works the best.  This decreases the likelihood of contamination, also.
 
Large Size7"x 11"
 
Fold Over and Sew End Seams
 
 
Half a Pipe Cleaner Sewn Into Upper Seam.  1/8" Elastic, 7" Long On Each End.
 
Fold Up and Sew Bottom, Catching Elasticat Corners.  Reinforce Stich on Elastic
 
Three Tucks On Each End (Folded the Same Way).  Sew on Each End.

A View of One End of the Mask Illustrating the Folds
 
And Here Is Paul Modeling the Mask.