Unicorn 3B — Mushroom Substrate Fruiting Bag (Large) *high gas exchange*
The Unicorn 3B is a large mushroom substrate fruiting bag built around the breathable B filter — the choice for growers who need maximum gas exchange during colonisation. The same trusted bag dimensions as the 14A, but with a 5 micron B filter that promotes faster, freer air exchange. Made in the USA since 1990 by Unicorn Bags LLC, the industry's most trusted name in mushroom cultivation bags.
Specifications
- Filter: 5 micron B filter — high gas exchange, promotes fresh air exchange for species sensitive to CO₂ build-up
- Capacity: Up to 5 lbs (~2.3kg) of substrate
- Size: 19" × 8" × 5"
- Material: 2.5 mil polypropylene — autoclave and pressure cooker safe at 121°C / 15 PSI
- Side-gusseted, reinforced bottom seal
Why Growers Choose the 3B
- The B filter's 5 micron pore size delivers high gas exchange — ideal for species that need strong fresh air exchange and are sensitive to CO₂ build-up
- Same trusted dimensions as the 14A in a slightly lighter 2.5 mil polypropylene construction
- 2.5 mil polypropylene handles autoclave and pressure cooker cycles without warping or seal failure
- Trusted by hobbyists + commercial growers worldwide
Prefer a more balanced gas exchange option? The 14A uses a 0.5 micron A filter for versatile use across the widest range of species. Ready for more volume? The XLS-A is built for high-volume production.
Need grain spawn bags instead? See our spawn bag range.
The 3B is the bag of choice when high gas exchange is the priority. In stock & dispatched quickly from our UK warehouse.
Find your bag
Which fruiting bag is right for you?
| Unicorn 4A | Unicorn 10A | Unicorn 14A | Unicorn XLSA | Unicorn 3B | Unicorn XLSB | |
|---|---|---|---|---|---|---|
| Type | Substrate | Substrate | Substrate | Substrate | Substrate | Substrate |
| Capacity | Up to 1kg (~2.2 lbs) | Up to 1.8kg (~4 lbs) | Up to 3kg (~6.6 lbs) | Up to 6.8kg (~15 lbs) | Up to 3kg | Up to 6.8kg |
| Filter | A - 0.5 micron | A - 0.5 micron | A - 0.5 micron | A - 0.5 micron | B - 5 micron | B - 5 micron |
| Best for | Small blocks, trialling species, tight spaces | Compact grows, stepping up from the 4A | Oyster, shiitake, lion's mane & more | High-volume & commercial production | High gas exchange requirements | High gas exchange requirements |
| Size | 4" × 3" × 18"10 × 8 × 46 cm | 5" × 4" × 18"13 × 10 × 46 cm | 8" × 5" × 19"20 × 13 × 48 cm | 10" × 5" × 24"25 × 13 × 61 cm | 8" × 5" × 19"20 × 13 × 48 cm | 10" × 5" × 24"25 × 13 × 61 cm |
| View | View | View | View | View | View |
All bags are polypropylene — autoclave & pressure cooker safe at 121°C / 15 PSI