Unicorn 4A — Mushroom Substrate Fruiting Bag (Small)

The Unicorn 4A is the most compact mushroom substrate fruiting bag in the range — the easy starting point for hobby growers, tight spaces and trialling new species without committing to a full-size block. Despite its size it's built to the same professional standard as the rest of the line, with a 0.5 micron A filter for clean, balanced gas exchange. Made in the USA since 1990 by Unicorn Bags LLC, the industry's most trusted name in mushroom cultivation bags.

Specifications

• Filter: 0.5 micron A filter — balanced gas exchange, maintains moisture retention during colonisation without over-drying your block
• Capacity: Up to 1kg of substrate
• Size: 4" x 3" x 18"
• Material: 3.0 mil polypropylene — autoclave and pressure cooker safe at 121°C / 15 PSI
• Side-gusseted, reinforced bottom seal

Why Growers Choose the 4A

• The smallest, lowest-cost way into Unicorn fruiting bags — ideal for hobbyists, testing and limited grow space
• The 0.5 micron A filter gives consistent gas exchange without the moisture loss that wider filters can cause
• 3.0 mil polypropylene handles autoclave and pressure cooker cycles without warping or seal failure
• Trusted by hobbyists + commercial growers worldwide

Ready to scale up? We also stock the 10A and the bestselling 14A for larger fruiting blocks, plus the XLS-A for high-volume production. Looking for grain spawn bags? We stock Unicorn spawn bags too — browse our full range.

The 4A is where many growers start with mushroom substrate fruiting bags. In stock & dispatched quickly from our UK warehouse.