What Is a Burlap Storage Sack? (Moisture Air Specs)
A burlap storage sack is a loosely woven bag, usually made from jute fiber, that lets air pass through more freely than an airtight container. It suits dry goods in dry, ventilated storage, but it is not a moisture barrier. There is no universal airflow or moisture rating: ask the supplier for test data and product-specific handling limits.
A breathable sack is useful only when the goods are dry
A burlap sack can help hold and move dry commodities while allowing air to pass through its weave. That same openness means humidity, spills, and damp floors can affect the contents. The sack alone cannot keep stored goods dry.
The term “burlap” commonly refers to a coarse woven fabric made from jute, though the exact fiber, weave, finish, and construction can vary by product. I use one practical test when comparing sacks: can the seller document what the bag is made of, how it was treated, and how its airflow or moisture performance was tested? If not, avoid assuming its specifications.
Material Selection and Sack Preparation
Start by matching the sack to the contents and the storage period. Jute burlap is a breathable fabric, not a sealed container. Since fiber, weave, stitching, and coatings affect performance, check the individual product rather than treating all burlap sacks as equivalent.
What a burlap storage sack is made from
A burlap sack is a bag made from coarse woven fabric, often jute. “Woven” means strands cross over and under one another, leaving spaces that can let air and water vapor pass. How much passes depends on the fabric and test conditions.
Before buying, confirm the intended commodity, capacity, dimensions, and supplier’s care instructions. Ask whether the sack is coated, dyed, treated for pests, or made with any finish that could transfer to the contents. A sack that looks plain is not proof that it is untreated.
Jute’s commonly cited commercial moisture regain is about 13.75% under standard textile-conditioning conditions. Moisture regain is a way of describing water held by a fiber relative to its dry mass. It is not a safe moisture target for grain, seeds, or other stored food.
Food contact and cleanliness
A sack is not automatically suitable for food contact just because it is made from a natural fiber. Food-contact suitability depends on the sack’s cleanliness, treatments, and supplier documentation. If contents will be eaten, ask the supplier for written confirmation that the product is suitable for that use.
Use a sack that is dry and free of stains, mold, musty odor, or chemical smells. Reject one with an unknown residue or history. For a new sack, follow the supplier’s instructions; washing or wetting it may affect its construction or leave it damp for storage.
How to compare technical specifications
Air permeability describes how much air passes through fabric under stated test conditions. Water-vapor transmission describes how much water vapor passes through a material over time. Neither is a single fixed property of every burlap sack.
| What to request | Useful detail | What it tells you |
|---|---|---|
| Air permeability | ISO 9237 or ASTM D737 report; pressure differential and units | Airflow through the tested fabric under those conditions |
| Water-vapor transmission | ASTM E96/E96M report; test method and conditions | Water-vapor movement through the tested material |
| Construction details | Fiber, weave, coating, seam, and closure information | What the sack is made of and how it is assembled |
| Food-contact information | Supplier documentation for the intended commodity | Whether the product is appropriate for that use |
There is no universal burlap airflow or moisture rating. Results from ISO 9237 and ASTM D737 are not directly interchangeable unless test conditions match. Also, a test on fabric may not describe the finished sack: seams, closures, and coatings can affect performance. Request product-specific data if a measured value matters.
Filling, Ventilation, and Moisture Control
A breathable sack can support air movement, but it cannot correct wet contents or a humid storage area. Fill it only with goods that meet their own moisture limits, and keep it in a cool, dry, pest-managed place. Watch for dampness, heating, clumping, or odor.
Prepare the goods before filling
Confirm the commodity’s moisture limit for the intended storage period and conditions. Limits vary by product, temperature, and duration. As one example, long-term grain storage commonly calls for grain dried to roughly 13% moisture or lower, but that is not a universal rule for every grain or situation. Check guidance for the specific commodity.
Do not use the jute fiber regain figure as a food-moisture target. The two numbers describe different things: one concerns water held by textile fiber, while the other concerns moisture in a stored commodity.
Use this sequence:
- Confirm what will be stored, for how long, and under what conditions.
- Check supplier treatment and food-contact information, if relevant.
- Confirm the commodity-specific moisture limit.
- Inspect the dry sack and dry goods before filling.
- Close the sack without blocking ventilation that the storage plan requires.
Airflow and moisture are not the same
Air passing through a weave does not guarantee that the contents will stay dry. Humid air can carry moisture into a sack, and a porous fabric does not stop moisture migration. Burlap should not be treated as waterproof, airtight, or vapor-proof.
A plastic liner may seem like added protection, but it can trap moisture and worsen condensation if the goods are not sufficiently dry. Do not place damp food in a sealed plastic-lined burlap sack. If a liner is needed for a specific use, confirm the storage method with the commodity supplier and avoid sealing in moisture.
Illustrative storage cases
These examples show how the decision changes with the conditions; they are not test results or guarantees.
Case 1: Dry grain in a ventilated store. A homeowner plans to store grain long term. They check the grain’s moisture against guidance for that grain and storage period, then choose a clean sack and keep it off the floor and away from walls. Burlap may be suitable if the setting is dry and pest-managed, but the sack does not replace moisture checks.
Case 2: Produce with surface dampness. A worker places recently washed produce into a sack. Even if the fabric breathes, damp contents and humid air may encourage spoilage. The safer step is to dry the produce as appropriate for that commodity and use a storage method designed for it.
Case 3: A damp shed and a plastic liner. A DIY builder sees condensation near a stack of lined sacks. The liner may be trapping moisture, while the surrounding area is humid. They should remove affected goods, assess the contents, and correct the storage conditions rather than assuming another layer of plastic will solve the problem.
Inspection, Cleaning, and Reuse
Routine checks help catch moisture problems before they spread. Inspect both the sack and its contents, and respond to warning signs promptly. A sack that is moldy, contaminated, or persistently musty should not be reused for stored goods.
What to inspect and when to act
Check sacks and contents routinely, with frequency suited to the commodity and storage conditions. Look for wet spots, condensation, stains, clumping, unusual warmth, insects, and musty or chemical odors. These signs call for investigation; they do not by themselves identify the cause.
If contents feel damp, appear to be heating, or develop clumps or a musty smell, empty the sack promptly and assess the goods. Do not rely on the bag’s airflow to dry them. Follow safe handling guidance for the commodity, especially if mold or spoilage is suspected.
Keep sacks off floors and away from walls, where contact with damp surfaces can transfer moisture. Store them in a cool, dry area and manage pests according to the needs of the goods. Avoid stacking or enclosing them in a way that blocks the ventilation required by the storage plan.
Cleaning and reuse
Empty reusable sacks promptly after use. Follow the supplier’s cleaning instructions, then let the sack dry fully before reuse. Do not put a damp sack back into storage or fill it with dry goods.
Discard a sack with mold, chemical contamination, or a persistent musty odor. Brushing off visible mold does not establish that the fabric is safe for reuse. If the sack held a treatment or substance that could contaminate the next load, do not reuse it for food.
Storage, Handling, and Serving Presentation
Burlap can be used to hold dry goods for storage or transport when the sack and setting suit the contents. Its rustic look does not prove food safety, and its open weave does not provide a moisture barrier. Choose appearance only after confirming the practical requirements.
Placement, handling, and display
Keep filled sacks in a dry, pest-managed area, away from walls and floors. Handle them so seams and closures are not strained, and follow supplier limits for filling and lifting. No single capacity or safe load applies to all sacks; fabric, stitching, dimensions, and condition differ.
For display, use a sack only when its cleanliness and treatment are suitable for the intended contact. A decorative burlap sack placed near food is not necessarily safe for direct food contact. If the contents are not documented as food-contact suitable, keep them separate from the fabric.
Quick selection guide
| Situation | Is a burlap sack a reasonable choice? | Key check |
|---|---|---|
| Dry goods in a dry, ventilated space | Often, if the sack suits the commodity | Confirm storage moisture limits and sack condition |
| Goods that may be damp or wet | No, not as moisture protection | Dry goods and choose a suitable storage method |
| Storage where humidity is uncontrolled | Not without further assessment | Check the environment and commodity guidance |
| Food contact | Only if documented as suitable | Ask about cleanliness, treatment, and supplier approval |
| A need for a measured airflow value | Only with product-specific evidence | Request ISO 9237 or ASTM D737 results and conditions |
The key decision is not whether burlap “breathes” in general, but whether the specific sack and storage conditions suit the goods. Confirm the material and any test data, start with dry contents, and inspect regularly.
Frequently Asked Questions
Is a burlap storage sack waterproof?
No. Burlap is a porous woven fabric and should not be treated as waterproof or vapor-proof. Water, humid air, or a damp surface can affect the sack and its contents. Use a storage method designed to protect goods from water when that protection is required.
Does burlap have a standard airflow rating?
No universal airflow rating applies to every burlap sack. Weave, yarn, coatings, seams, and test conditions change results. Ask the supplier for an ISO 9237 or ASTM D737 report that states the pressure difference and units.
What does 13.75% moisture regain mean?
It is a commonly cited commercial value for moisture held by jute fiber under standard textile-conditioning conditions. It describes the fiber, not the food inside a sack. Do not use it as a safe moisture limit for grain or other stored goods.
Can I store grain in a burlap sack?
Possibly, if the grain is dry enough for its type and storage period and the area is cool, dry, and pest-managed. Long-term grain storage commonly requires moisture around 13% or lower, but the safe limit depends on the grain and conditions.
Can I use a plastic liner inside burlap?
A liner can trap moisture and increase condensation risk if goods are not sufficiently dry. Do not seal damp food inside a plastic-lined sack. Check the commodity’s storage guidance and the liner’s suitability before using one.
How do I know if a burlap sack is safe for food?
Ask the supplier for written information on food-contact suitability, cleaning, and treatments. A natural-fiber label does not confirm that a sack is clean or untreated. Reject sacks with mold, stains, chemical odor, or an unknown contamination history.
Can I reuse a burlap storage sack?
Yes, if the supplier permits reuse and the sack is clean, dry, and free of contamination. Empty it promptly and let it dry fully before refilling. Discard sacks with mold, chemical contamination, or a persistent musty odor.
What should I do if a sack or its contents become damp?
Empty the sack promptly and assess the goods. Check for condensation, clumping, heating, or musty odor, and follow safe handling guidance for the commodity. Dry reusable sacks fully before reuse; discard moldy or contaminated sacks.
(This article was written by one of our staff writers, Julian R. Hayes. Visit our Meet the Team page.)
