For people that don't know what they are, their "silk screens" that come in various "microns" which measure the size of the spaces in the fabric (25 Micron, 75m, 90m, 100m, 110m, 150m, 200m, 220m(keif grade hash)).
You use these bags along with ice water, or dry ice and the result is "Bubble hash".
If you already knew that, and want to know EXACTLY what a "Bubble bag" is, then the rest is for you.
bags are actually what is called a "silk screen" which is used to print
ink designs onto shirts, posters, etc. but someone figured out that it
not only filters ink, but marijuana :D
So the part of the bag that is important, and measured in microns is actually a "Silk Screen".