these filter bags are the highest quality and lowest cost solution for your rosin press! The micron rating represents the maximum size of the particle that can pass through the filter material. The bag stitching is color coded with FDA food grade dyed polyester monofilament so that you always know which mesh you are working with! All of the bags are tube shaped to promote the highest yields by minimizing the distance the oil has to travel to escape the rosin bag. Simply fill it up, fold over the end and you are ready to press.