A cultivation bag assembly for the cultivation of microbes, fungi and other organisms includes a bag having first and second walls joined along side edges to define a bag interior for containing a food substrate and an organism to be cultivated. At least one of the first and second walls is constructed of a layer of water-vapor permeable material to allow the passage of water vapor therethrough. A bag wall overlay layer formed from gas impermeable layer is releasably coupled to the bag. The overlay layer overlays the layer of water-vapor permeable material to prevent the passage of gases therethrough. The bag wall overlay layer has an opening with a gas filter patch covering the opening to allow the passage of oxygen and carbon dioxide gases through the gas filter patch to and from ambient air to facilitate incubation of the organism within the interior of the bag. The bag wall overlay layer is removable from the bag to allow water vapor to pass through the layer of water-vapor permeable material to ambient air facilitate drying of the bag contents after incubation is complete.
