Mushroom substrate jars are a popular choice for many home growers because they have a lesser chance of becoming contaminated when compared to grow bags. Jars also colonize very fast, usually within 3 weeks. Each jar lid features a self-healing injection port and synthetic .22 micron gas exchange filter. All of our substrates jars are made-to-order and shrink wrap each jar to lock in freshness. 

Mushroom substrate bags are less expensive than jar substrates because they weight less than glass and are cheaper to ship . Sometimes bags are subject to contamination because there may be a defect in the bag like a pinhole or bad heat seal in the bag. For the most part bags are reliable but just be gentle with them and not force air in and out of the bag and you should be good.