I appreciate CO finest's help, tutorials and videos too...but, if I may also;
Dry ice extraction has some of the highest levels of contaminant (i.e. anything other than glandular trichome heads) of any extraction method out there. The dry ice makes everything in the bag so cold and brittle that even very large amounts of plant matter can break up into small enough particles to pass through the screen, regardless of micron size of the holes. That is why the ice-water-extraction method is still one of (if not THE) best extraction methods for the connoisseur. The dry ice method is fast and a decent way to reduce your volume into more portable, easily-stored sized containers, but the final product should still be carded to remove those unwanted contaminants. I am in no way an expert, however, I have read literally volumes on extraction methods and have personally practiced; Dry ice extraction, ice water extraction, BHO (with blast tubes and vac-purges), QWISO, RSO.
The best method for purity of end product, for me anyway, is the ice/water mesh-bag method. Though water is a solvent too, it's still considered to be solventless, yet WAY less labor-intensive than dry-sifting. I like my hashes, and they all turn to liquid when heat is applied.
O.K., sorry for the interruption. Here's your soap box back now...lol.
p.s. The smallest micron bag in the set is rarely the best quality of hash. Usually, it's in the 73u bag or the 45u bag. My last 2 bubblebag runs had the highest yield in the 45u bag. The bag with the highest yield is strictly dependant upon strain and ripeness. Sativa strains genetically have smaller glandular heads so theirs will settle in the lower bags, and if not allowed to achieve complete maturity, all glandular heads will not be completely swollen or developed and they too will settle in the lower bags. Just saying.