Sakato Mushroom Grow Bags are meticulously designed as the ideal grow bag for fruiting blocks. These bags are made with your choice of opaque or black polyethylene that is sturdy enough for anything you can throw at it. The grow bag comes with a 25 mm diameter, 5-micron filter patch for optimal gas exchange and protection against contamination, turning your substrate block into its own separate biome. Polyethylene materials limit light to prevent premature fruiting/pinning.