Filter Bag XL

Filter Bag XL for Mushroom Growing

The Filter Bag XL is a polypropylene mushroom grow bag designed for 2100ml substrate kits, fitted with 4 built-in filter strips that vent CO2 while locking in moisture and blocking contaminants. If you're running larger batches or working with bigger grain jars, this is the bag that actually fits the job without you having to jury-rig something smaller.

Why You Need Proper Filter Bags for Mushroom Cultivation

Contamination is the number one reason home grows fail. It's gutting, and it's almost always avoidable.

The problem is simple. Mycelium needs to breathe — it produces CO2 as it colonises substrate, and that gas needs somewhere to go. But the moment you open a path for gas exchange, you also open a path for airborne contaminants: mould spores, bacteria, dust. A standard bag can't do both jobs. A filter bag can. The micro-porous filter strips on the Filter Bag XL allow CO2 to vent out while the pore size is small enough to block contaminants from getting in. At the same time, the polypropylene holds moisture inside the bag, keeping your substrate at the humidity level mycelium actually wants.

The honest limitation? Filter bags aren't reusable forever. Each autoclave cycle stresses the material slightly, and after a few rounds the seal integrity drops. We'd treat these as single-use or 2-use maximum to be safe. The cost per bag is low enough that it's not worth risking a whole batch over a worn-out filter strip.

How to Use the Filter Bag XL

1. Prepare your substrate or grain mixture and load it into the Filter Bag XL. The bag accommodates up to 2100ml of substrate comfortably — don't overfill past the filter strip line or you'll block the gas exchange.
2. Seal the bag using an impulse sealer. Position the seal above the filter strips so the 4 micro-porous panels remain unobstructed between the substrate and the sealed top.
3. Autoclave the entire sealed bag at 121°C (15 PSI) for 60–90 minutes to sterilise the substrate inside. The polypropylene material is rated for autoclave temperatures, so it won't warp or melt.
4. Once cooled to room temperature, inoculate through a small self-healing injection port or by briefly opening the top in front of a laminar flow hood. Reseal immediately.
5. Store the inoculated bag in a clean, dark space at 22–25°C. The filter strips will passively vent CO2 while maintaining internal humidity. You should see visible mycelial growth within 7–14 days depending on the species and spawn rate.
6. Once fully colonised, open the bag and transfer to your fruiting chamber, or — if you're fruiting in-bag — cut the top open and mist as needed.