How to Build and Use a Still Air Box (SAB)

If you want to grow mushrooms beyond the kit stage, you need a way to work with cultures without introducing contamination. That means agar plates, liquid culture syringes, grain jars, and spawn transfers. Every one of those tasks requires a clean environment where airborne contaminants are kept away from your work.

A still air box (SAB) is the simplest, cheapest solution. For under $15 and about 20 minutes of work, you can build one that will serve you for years. We've used SABs to do everything from pouring agar to inoculating dozens of grain jars, and our contamination rates stay consistently low when proper technique is followed.

This guide covers the full build, the technique that makes it work, and common mistakes that trip up beginners.

What Is a Still Air Box?

A still air box is exactly what it sounds like: a clear plastic tub turned upside down with two arm holes cut into one side. You reach inside through the holes, and the enclosed space prevents air currents from carrying contaminants onto your work.

Unlike a laminar flow hood, an SAB doesn't filter air. It works on a different principle entirely. In still air, contaminant particles settle downward due to gravity rather than floating around. As long as you don't create air currents inside the box (by moving too quickly, for example), those particles stay settled on the bottom and sides of the tub rather than landing on your agar plates or grain jars.

It's a low-tech approach, but it works remarkably well. Experienced growers routinely achieve contamination rates under 5-10% using a properly built and properly used SAB. That's good enough for any hobbyist and many small-scale commercial operations.

Why You Need One

If you're doing any of the following, you need either an SAB or a flow hood:

• Pouring or inoculating agar plates — agar is nutrient-rich and exposed. Without protection, mold spores land on it within seconds.
• Making or working with liquid culture — inoculating LC jars or drawing syringes from them exposes the liquid to open air.
• Inoculating grain jars — opening a sterilized grain jar outside of a clean environment is an invitation for Trichoderma and other contaminants.
• Doing grain-to-grain transfers — pouring colonized grain into fresh jars requires both jars to be open simultaneously.
• Cloning mushrooms — tissue culture involves cutting a small piece of mushroom and placing it on agar. Sterile conditions are essential.

You don't need an SAB for fruiting, harvesting, mixing substrate, or anything that happens after full colonization. The SAB is specifically for the vulnerable, sterile stages of cultivation.

Materials List

Here's everything you need. Total cost is typically under $15 CAD. If you add the optional extras below (gloves and a torch), the full kit lands closer to $40-60 CAD — still a fraction of the cost of a flow hood.

Item	Estimated Cost	Notes
Clear plastic tub (64-106 qt / 60-100 L)	$8-12	Sterilite or similar. Must be clear so you can see your work. Taller is better — you want room to maneuver inside.
Hole saw or soldering iron	$0-5	A 10-13 cm (4-5 inch) hole saw attachment for a drill works best. A soldering iron or heated can also work.
Masking tape or marker	$0	For marking hole positions.
Isopropyl alcohol (70%)	$3-5	For sanitizing. You likely already have this.
Paper towels	$0	For wiping down the interior.
Nitrile gloves	$10-15 (box of 100)	Snug fit; wipe gloved hands with alcohol before every session.
Butane torch or lighter	$10-15	For flame-sterilizing scalpels and syringe needles between transfers.
Arm-length gloves (optional)	$10-20	Shoulder-length disposable gloves for extra coverage; most growers do fine with nitrile + alcohol-wiped forearms.

Optional but helpful:

• A small towel or mat to place inside the tub so items don't slide
• A spray bottle for the isopropyl alcohol
• Nitrile gloves

Step-by-Step Build

Step 1: Choose Your Tub

Look for a clear plastic storage tub in the 64-106 quart (60-100 litre) range. The Sterilite 106 qt tub from Canadian Tire or Walmart is a popular choice. You want it to be:

• Clear — you need to see what you're doing through the walls and lid
• Tall enough — at least 30 cm (12 inches) tall so you have room to work
• Wide enough — you'll have your arms inside, plus agar plates, a lighter, a scalpel, and whatever else you're working with

Step 2: Mark Your Arm Holes

Flip the tub upside down (the bottom facing up). The open side will face down toward your work surface when you use it.

On one of the long sides, mark two circles about 10-13 cm (4-5 inches) in diameter. Space them roughly shoulder-width apart, positioned in the lower half of the side wall. You want the holes low enough that your hands reach the bottom of the tub (which is now the top) comfortably.

Some growers put the holes on the bottom (now the top) of the tub instead. This works but makes it harder to see your work. Side-mounted holes are generally preferred.

Step 3: Cut the Holes

Hole saw method (recommended): Attach a 10-13 cm hole saw bit to your drill. Support the tub so the plastic doesn't flex too much, and drill through at moderate speed. The hole saw gives you a clean, round hole.

Soldering iron method: Heat the soldering iron and slowly melt through the plastic along your marked circle. This works but produces fumes — do it outside or in a well-ventilated area. The edges won't be as clean.

Hot can method: Heat an empty tin can on the stove and press it through the plastic. Crude but effective in a pinch.

Step 4: Smooth the Edges

Sand or file any rough edges around the holes. You'll be sliding your arms in and out, and sharp plastic edges will scratch you up. A few passes with fine-grit sandpaper is all it takes.

Step 5: Clean and Sanitize

Wipe down the entire interior of the tub with 70% isopropyl alcohol. Pay attention to corners and edges where dust accumulates. Let it air dry — 70% iso evaporates quickly.

That's it. Your SAB is built.

The box itself

How to Use Your SAB: Proper Technique

Building the box is easy. Using it correctly is where most contamination happens. Here's the technique that keeps your work clean.

Setting Up Your Workspace

1. Choose a calm room. Turn off fans, close windows, shut off HVAC vents if possible. Any air current in the room is an air current inside your SAB. A bathroom or small room with the door closed works well.

2. Clean the room. Give the surfaces a quick wipe. Some growers spray Lysol in the room 15-20 minutes before working to knock airborne particles out of the air. Let it settle — don't work in a cloud of Lysol.

3. Prepare everything outside the box first. Get all your materials ready: agar plates, scalpel, lighter or alcohol lamp, parafilm, grain jars, syringes — whatever you're going to need. Arrange them on the table in front of you.

4. Wipe down the SAB interior with 70% iso and let it dry.

5. Wipe down every item that goes into the SAB. Jars, plates, tools, lighter, your gloved hands — everything gets a wipe or spray with iso.

6. Place items inside. Put everything into the SAB from the open bottom, then lower the tub over your workspace. Some growers prefer to put items in through the arm holes, but loading from underneath before flipping/lowering is easier.

Working Inside the SAB

This is where discipline matters.

Move slowly. Fast movements create air currents that stir up settled particles. Every reach, every pour, every movement should be deliberate and unhurried. Think of it like working underwater — smooth, controlled motions only.

Keep your arms still when not actively working. Your arms are pistons in the arm holes. Every time you move them, you pump air in and out of the box. Insert your arms, let the air settle for 30 seconds, then begin working.

Flame sterilize your scalpel and needle. Before every cut and every inoculation, heat your scalpel blade or needle in a flame until it glows red. Let it cool for a few seconds (don't blow on it — that defeats the purpose). This is non-negotiable, even inside the SAB.

Work near the bottom of the tub. Contaminants settle downward. The higher up in the SAB you work, the cleaner the air. Since the tub is flipped, the "top" of your workspace (the original bottom of the tub) is the cleanest zone.

Don't cough, sneeze, or breathe directly toward your work. Some growers wear a surgical mask. At minimum, turn your head away from the arm holes if you need to cough.

Open plates and jars for the minimum possible time. Have your inoculant ready, open the lid, do your work, close the lid. Seconds, not minutes.

Specific Tasks in the SAB

Agar work: Pour plates, inoculate with spore syringes, transfer cultures, and clone mushroom tissue inside the SAB. Have your parafilm strips pre-cut and ready. Seal each plate immediately after work.

Liquid culture inoculation: Shake your liquid culture jar, flame your needle, pierce the injection port, draw or inject, remove needle, done. Keep the jar upright the entire time.

Grain jar inoculation: Flame your needle, inject through the port or crack the lid just enough to insert the needle, inject 1-2 cc of liquid culture per jar, reseal immediately.

Common SAB Mistakes

We see these over and over, especially from growers who are getting consistent contamination:

Moving too fast. This is the number one mistake. Speed creates air currents. Slow down.

Not letting the air settle. After you put your arms in, wait. Thirty seconds minimum. The air you displaced needs to settle.

Working in a drafty room. The SAB doesn't seal airtight around your arms. If there's a draft in the room, it's getting into the box. Close windows, shut off fans, close the door.

Skipping flame sterilization. The scalpel touched the side of the tub? Flame it. The needle brushed your glove? Flame it. When in doubt, flame it.

Reaching in and out repeatedly. Every time you pull an arm out and put it back in, you create a piston effect that pushes and pulls air. Get everything you need inside the box before you start, and work through your batch without removing your arms.

Not wiping items down. That grain jar just came out of the pressure cooker and looks sterile, but the outside of the jar was exposed to room air. Wipe it with iso before it goes in the SAB.

Cluttered workspace. Too many items inside the SAB means more things to bump, more air currents, and less room to work. Only put in what you need for the current task.

SAB vs Flow Hood: A Quick Comparison

Feature	Still Air Box	Laminar Flow Hood
Cost	$10-15	$300-800+
Setup time	20 minutes	Hours (if building)
How it works	Gravity settles particles	HEPA filter removes particles
Contamination rate	5-10% (with good technique)	1-2%
Best for	Hobbyists, small-batch work	Scaling up, high-volume
Portability	Easy to store anywhere	Bulky, semi-permanent
Learning curve	Technique-dependent	More forgiving

For most home growers, an SAB is all you'll ever need. If you're making dozens of plates or jars per session, or if you're starting to scale toward a commercial operation, a flow hood becomes worth the investment. We have a full breakdown in our flow hood vs SAB comparison.

Tips for Better SAB Results

Use an alcohol lamp instead of a lighter. An alcohol lamp provides a continuous flame and an updraft of warm air above it. That rising air column creates a small sterile zone. Position your work near (but not directly over) the flame for an extra layer of protection. You can make an alcohol lamp from a small glass jar, a cotton wick, and 70% iso or high-proof alcohol.

Dampen the inside walls. A light mist of water on the inside walls of the SAB helps trap airborne particles on the plastic surface rather than letting them float.

Work at night. There are fewer airborne contaminants circulating when the house is quiet — no one walking around, no doors opening, no cooking.

Batch your work. Rather than opening and closing the SAB repeatedly over several days, do all your agar transfers, inoculations, and culture work in a single session.

Keep a clean tub. After each session, wipe the SAB down with iso and store it inverted (holes facing down) to keep dust out.

Your First Projects Inside the SAB

The box is built, the room is calm, and your gloved hands are wiped down. So what should you actually do in there first? These two projects are the classic starting points. Both are forgiving enough for a first session, and both teach the slow, deliberate movements that every later technique depends on.

Agar-to-Agar Transfers

Transferring a wedge of healthy mycelium from one plate to a fresh one is the fundamental skill of culture work, and the SAB is the perfect place to learn it. Set both plates inside the box — the colonized plate and a fresh one — along with your scalpel, flame, and pre-cut parafilm strips. Flame the scalpel blade until it glows, then let it cool for a few seconds (touching a corner of the fresh agar is a quick way to confirm it won't melt a trench). Open the colonized plate just enough to cut a small wedge from the growing edge of the mycelium — the newest, most vigorous growth, not the older centre. Lift the wedge, crack the lid of the fresh plate, and place it mycelium-side down in the middle. Close and seal with parafilm right away.

If you don't want to pressure-cook and pour your own plates yet, pre-poured plates from our agar category skip that step entirely — the LME Agar Plates 6-Pack is a ready-to-use starting point, so your first SAB session is all transfer practice and no prep. Once your plates are coming out clean, the same transfer discipline applies directly to grain-to-grain transfers. And cloning a mushroom is really just this same transfer with a piece of mushroom tissue as the source instead of a wedge of agar.

Liquid Culture Inoculation

The second classic first project is inoculating a liquid culture jar, either from a clean agar wedge or from a culture syringe. If you're working from a syringe: shake it well to distribute the mycelium, flame the needle until it glows, let it cool, then work through the jar's injection port — no need to open the lid at all. Inject 1-2 cc, withdraw the needle, and wipe the port with alcohol. If you're transferring from agar, cut a small wedge exactly as described above, crack the LC jar's lid just wide enough to drop it in, and reseal immediately.

Keep everything low and slow inside the box. The jar stays on the work surface, your movements stay smooth, and lids come off for seconds, not minutes. A purpose-made vessel makes this much easier for a first attempt: the Sterile LC Expansion Jar comes pre-sterilized with an injection port and breathable filter already installed, so there's no canning or lid-modifying required — you supply the culture, it supplies the clean container. Browse our cultures category if you'd rather start from a lab-isolated culture than a spore syringe; isolated cultures colonize faster and behave more predictably, which makes your first LC a lot more satisfying.

What You Can Do With an SAB

Once you have a working SAB, the entire upstream side of mushroom cultivation opens up to you:

• Pour and inoculate agar plates to isolate clean cultures
• Make and inoculate liquid culture
• Clone your best mushrooms onto agar
• Inoculate grain spawn jars and bags
• Do grain-to-grain transfers to multiply your spawn
• Work with spore prints and spore syringes

A $15 tub with two holes in it is genuinely all that stands between you and self-sufficient mushroom cultivation. Build one this weekend, grab some agar plates from our shop, and start learning. The technique takes a few sessions to dial in, but once you've got it, you'll wonder why you ever bought pre-made syringes.

The other tote worth drilling is a shotgun fruiting chamber, which handles fruiting the same way this box handles transfers.

An open flame inside a sealed tote is awkward, which is why disposable loops suit a still air box better than nichrome. See inoculating loops and agar tools.

Still Air Box FAQ

How big should the arm holes be?

Aim for 10-13 cm (4-5 inches) in diameter — big enough to slide your forearms in and out without scraping, small enough to limit air exchange. Space them roughly shoulder-width apart so your arms sit naturally, and position them in the lower half of the side wall so your forearms rest comfortably while your hands reach the work surface. If the holes force you to hold your arms up at an awkward angle, you'll fatigue quickly and start making rushed movements.

Do I need arm-length gloves, or are bare arms okay?

Bare forearms wiped down with 70% isopropyl alcohol are the standard approach, and most growers get clean results this way. The non-negotiable part is nitrile gloves on your hands, re-wiped with alcohol as you work. Arm-length disposable gloves are an optional comfort upgrade — some growers like the extra coverage, others find they reduce dexterity. If your contamination rates are good with bare wiped forearms, there's no reason to change.

How often should I wipe down with alcohol?

Wipe every surface — the SAB interior, every jar and tool going in, and your gloved hands — before each session. While working, re-wipe your gloves between plates or jars, especially after touching anything that isn't part of the current transfer. And any time you pull your arms out of the box and put them back in, wipe your gloves again before resuming. It feels excessive at first; it becomes automatic within a few sessions.

How do I clean and store my SAB between sessions?

Wipe the entire interior with 70% isopropyl alcohol at the end of each session and let it dry fully before putting it away. Store the tub upside down (holes facing down) or with the lid on so dust can't settle on the interior surfaces you worked so hard to keep clean. Never store it damp — trapped moisture in a closed plastic tub is an invitation for exactly the kind of growth you don't want.

When should I upgrade to a laminar flow hood?

Upgrade when volume makes the SAB the bottleneck — if you're pouring dozens of plates or inoculating dozens of jars every week, the slow pace of SAB work starts costing you real time. Don't upgrade because of contamination at hobby scale; that's almost always a technique problem a flow hood won't fix. Our flow hood vs still air box comparison breaks down the costs and the crossover point in detail.

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