The mushroom filter bag is a 1200ml polypropylene mycology grow bag that lets home cultivators sterilise their own substrate, inoculate with mycelium, and colonise a bulk block without inviting every airborne mould spore to the party. You fill it, you autoclave it, you inoculate it — the micro-porous filter strip handles gas exchange so your mycelium breathes without contamination creeping in.
What a mushroom filter bag actually is
A mycology filter bag is an empty, heat-resistant cultivation sleeve with a built-in 0.2 micron filter patch. It's not a grow kit, not pre-inoculated, and there's no substrate inside when it arrives — that's the whole point. You supply the grain, sawdust, or CVG mix, sterilise the lot at 121°C in a pressure cooker or autoclave, cool it down, and inoculate through the filter or a self-healing injection port (if you add one).
The filter does two jobs at once: it vents CO2 out (mycelium produces a lot of it during colonisation) and blocks spores, bacteria, and fungal contaminants coming in. Without that membrane, you're either suffocating your culture or inviting Trichoderma to ruin your week.
Why the mushroom filter bag beats jars and tubs
Mason jars cap out around 500ml of usable substrate and take up shelf space like nobody's business. A single 1200ml mushroom filter bag holds more than double that, flat-packs when empty, and goes straight into the pressure cooker without a lid to unscrew or a polyfil disc to fiddle with. Ten bags in one autoclave run is normal. Ten jars? You're doing two rounds.
The other win is contamination rate. Jar lids with micropore tape fail. Tubs without filtered lids pull in contaminated air every time the substrate cools. The filter patch on a proper mycology grow bag is factory-welded — no tape lifting, no gaps where the mask meets the lid. For anyone scaling past their first few grows, bags are just the sensible move.
Filter bag vs filter bag XL — which size
This is the standard 1200ml version. If you're running larger bulk substrate blocks or working with wood-loving species that want more room to spread, the filter bag XL (2100ml) is the bigger sibling. For grain spawn, smaller CVG blocks, or if you're still dialling in your process, the 1200ml is the one to grab.
| Use case | Recommended size |
|---|---|
| Grain spawn (rye, millet, wheat) | Filter bag 1200ml |
| Small bulk CVG block | Filter bag 1200ml |
| Large bulk substrate / wood lovers | Filter bag XL 2100ml |
| Master grain spawn for expansion | Filter bag XL 2100ml |
Specifications for the 1200ml mycology filter bag
| Capacity | 1200ml |
| Material | Polypropylene (food-grade) |
| Filter type | Micro-porous strip, approx. 0.2 micron |
| Max temperature | 121°C (autoclave / pressure cooker safe) |
| Closure | Open top — seal with impulse sealer, zip tie, or fold-and-tape |
| Use | Single use (do not re-sterilise after harvest) |
| SKU | SH0093 |
Why you need one (and not just a jar)
Contamination is the number one reason home grows fail. We've seen growers lose entire batches of grain because they trusted micropore tape on a jar lid that lifted during the cooldown. The filter bag removes that failure point — the filter is part of the bag, not stuck on with adhesive that softens at 121°C.
The other practical thing: you can squeeze, massage, and shake a bag to break up clumps and distribute mycelium evenly across grain. Try that with a jar. The flexible polypropylene lets you knead the colonised substrate into a uniform block before transferring it to a fruiting chamber, which speeds up full colonisation and gives you more consistent flushes.
How to use a mushroom filter bag
- Fill the bag with your prepared substrate — grain, CVG, or wood-based mix. Leave roughly one-third of the bag empty at the top for gas exchange and shaking room.
- Fold the top over loosely or clip with a heat-safe clamp. Don't seal airtight yet — steam needs to escape during sterilisation.
- Sterilise in a pressure cooker or autoclave at 121°C for 90 minutes (grain) or up to 2.5 hours for larger bulk blocks.
- Let the bag cool completely inside the cooker. Opening a hot bag draws in unfiltered air — patience here saves grows.
- Move to a still-air box or in front of a flow hood. Inoculate with liquid culture or spore syringe through the filter patch, or fit a self-healing injection port if you prefer.
- Seal the top properly now — impulse sealer is cleanest, zip tie works, folded and taped is the budget option.
- Incubate at the temperature your species wants (around 24-26°C for most cubensis strains). Shake once mycelium reaches roughly 25% coverage to speed colonisation.
- Once fully colonised and consolidated, cut open and transfer to a fruiting chamber, or fruit in-bag by cutting a wide slit.
Pair your filter bags with a pressure cooker rated to 121°C, a proper still-air box for sterile inoculation, and liquid culture or spore syringes from our mycology shelf. If you're running larger blocks, grab the filter bag XL (2100ml) alongside these for a mixed workflow — grain spawn in the 1200ml, bulk substrate in the XL.
Honest limitations
A couple of things to know. First, these are single-use bags — polypropylene survives one autoclave cycle reliably; running it through a second time risks micro-tears you can't see. Second, the filter patch is the weak point if you're careless. Puncture it with a syringe needle too many times and you've opened a hole that contamination will find. Inoculate through the filter once or twice max, or add an injection port. Third, they're not a shortcut for poor technique — a bag won't save a substrate recipe that's too wet, under-sterilised, or inoculated in a kitchen without a still-air box.
Frequently Asked Questions
Is this a ready-to-grow mushroom kit?
No. This is an empty polypropylene mycology filter bag. You fill it with your own substrate, sterilise, and inoculate. If you want a pre-colonised kit where you just add water, look at our grow kit range instead.
Can I reuse the filter bag after harvest?
No — these are single-use. Polypropylene handles one autoclave cycle at 121°C reliably, but repeat sterilisation weakens the material and the filter strip, which massively raises contamination risk on the next grow.
How long do I sterilise the bag for?
For grain spawn, 90 minutes at 121°C (15 PSI) is standard. For larger bulk substrate blocks or wood-based substrates, run 2 to 2.5 hours. Always let the bag cool completely inside the pressure cooker before moving it.
Do I need a flow hood to use a mushroom filter bag?
No, a still-air box works fine for most home growers. The filter strip does most of the contamination blocking on its own — the still-air box just gives you a clean window during inoculation, which is when the bag is briefly open.
What's the difference between this and the filter bag XL?
Capacity. This one holds 1200ml, the XL holds 2100ml. The XL is better for larger bulk substrate blocks or master grain spawn; the 1200ml is the right call for regular grain spawn runs and smaller CVG blocks.
Can I inject spores or liquid culture directly through the filter?
Yes, once or twice through the filter patch is fine. For multiple inoculations or if you're doing grain-to-grain transfers, fit a self-healing injection port — it prevents the filter strip from developing puncture holes that let contamination in.
Last updated: April 2026
