Please excuse me if this isn't a physics question - I'm not sure where it belongs. Felt, such as this: http://www.ebay.com/itm/Felt-by-the...-36-INCHES-square-100-polyester-/261301533508 And 3mil plastic sheeting, as this: http://www.homedepot.com/p/Husky-8-Ft-x-100-Ft-Clear-3-mil-Plastic-Sheeting-CF0308C/202184057 -------- How small of a particle size, will those block? For example: if I throw a .3 micron particle at the felt, will it go through? How about the plastic? Thanks!