The 14A with XLS filter provides just the right amount of gas exchange/air flow for most top-fruiting strains to fully develop en vitro (without even needing to cut the bag for added oxygen). Some strains still prefer the cut bag at a certain point in fruit-body development, but size of cut still depends on the bag's external environment for humidity and sterility. Fruiting with these bags en vitro means you are less reliant on supplemental humidity like there is in most gourmet mushroom fruiting environments. It also allows fruiting en vitro in "dirtier" grow spaces with less opportunity for contamination.