Solventless extraction relies on mechanical separation to isolate resin glands from cannabis material. Dry sifting, pressing rosin, and washing bubble hash are different types of solventless extraction that requires extractors to sieve a trichome-rich starting material with some form of nylon mesh filter. Depending on what type of extraction you’re doing, the sieves are slightly different in form but virtually the same in function. 

For washing bubble hash, these sieves are called bubble wash bags. Bubble wash bags look like regular open-top bags with a mesh filter sewn into the bottom of the bag. Pressing rosin uses sieves called rosin filter bags, which resemble tea bags in appearance. And dry sifting involves a series of sieves called dry sifting screens, which stack one on top of the other and resemble regular window screens in size and shape. 

In each case, these filters are designed to hold cannabis material back, while allowing resin-packed trichome heads to pass through. And not only one size of filter is used. In fact, a variety of sizes of filters are appropriate for various purposes. So how do we measure the size of a filter, and differentiate between the fineness or coarseness of filters? 

The pore size in rosin bags and bubble wash bags is measured in microns, whereas the pore size in dry sifting screens is measured in LPI, or Lines Per Inch. 

A micron is a unit of measurement that equals 1/1000th of a millimeter. The micron of a rosin bag refers to the distance across each one of the tiny holes, or pores, that make up the filter. Smaller pores make the material feel finer, while larger pores make the material feel coarser. 

Measuring filters by microns gives us a measurement of the diameter of each pore. So, a 90 micron bubble wash bag indicates that each pore in the filter is 90 microns across. 

The more lines per inch, or threads, that there are in the filter, the smaller the pore size will be. Likewise, less threads in the material equates to a larger pore size. 

Here are the most common conversions for dry sifting screens:

60 LPI = 250 Microns *work screen
88 LPI = 165 Microns  
100 LPI = 149 Microns
199 LPI = 75 Microns  *often the best quality is collected from this screen 

Learn more about dry sifting, and how to use various sizes of dry sifting screens together, check out The Press Club's Ultimate Guide To Dry Sift.

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FREQUENTLY ASKED QUESTIONS

What does LPI mean?
LPI stands for Lines per Inch, and it's a way to measure the pore size in filters, commonly referred to as US Mesh. 

What is the best LPI screen for dry sifting?
The best LPI for dry sifting is in the range of 51-355 LPI. Multiple sifting screens are used together in order to properly isolate trichome heads. 

How do you convert microns to LPI?
The best way to convert microns to LPI is to use a conversion table like the image in this article. 

Why aren't dry sifting screens measured in microns?
Sifting screens are measured like nylon mesh, which in the US is commonly indicated in lines per inch. 

What LPI dry sifting screen size most closely matches the size of full trichome heads?
The 230 LPI screen, or 63 micron, is often the closest size to the trichome heads that dry sifting targets.