Micron bags are filter bags made of mesh with a precisely rated opening size, measured in microns (µm; 1 µm = 0.001 mm). In ice water hash making they are used in a nested set of different grades so that each bag retains a different size fraction of trichome heads while plant debris and water pass or are held back. Similar but smaller bags are used to contain material in a rosin press and filter the oil. Dry sift uses flat, framed screens on the same principle.
In practice
Hash makers label each collected fraction by the bag it came from, for example "90 µm" or "120 µm", because the fraction indicates head size and usually quality. The best fractions vary by cultivar, since head size is partly genetic. Mesh quality matters: inconsistent weave mixes grades. GenetixBay defines the equipment and gives no wash procedures.
Units and formula
Micron (µm) = one millionth of a metre. A 73 µm screen has openings 0.073 mm across.
Don't confuse with
- Mesh count (lines per inch): an older sieve rating that doesn't convert simply to microns.
- Rosin bags: the same principle, used for pressing rather than washing.
