MIL-PRF-131L
MIL-PRF-131 is the U.S. military performance specification for water vapor proof, grease proof, flexible, heat-sealable barrier materials. These foil-laminate materials are used to make sealed barrier bags that protect moisture-sensitive items during military storage, preservation, and transportation.
Arms Preservation Inc. (API) can offer MIL-PRF-131 barrier material as finished bags or roll stock for military, aerospace, defense, and industrial preservation requirements. API can accommodate custom packaging requirements, with availability and contract-specific documentation confirmed during quotation.
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What Is MIL-PRF-131?
MIL-PRF-131, officially titled "Barrier Materials, Watervaporproof, Greaseproof, Flexible, Heat-Sealable," establishes the performance requirements for flexible barrier materials with low water vapor transmission characteristics used in military packaging.
MIL-PRF-131 materials are typically laminates of plastic film, aluminum foil, and a heat-sealable polyethylene layer. The foil layer provides the primary barrier to water vapor.
Bags made from MIL-PRF-131 material are governed separately by MIL-DTL-117, the detail specification for heat-sealable bags.
This distinction is important: MIL-PRF-131 establishes requirements for the barrier material, while MIL-DTL-117 establishes requirements for the finished bag.
The specification began as MIL-B-131 and became a performance specification with MIL-PRF-131J in 1998. MIL-PRF-131K followed in August 2005 and is still widely cited in part numbers and solicitations. MIL-PRF-131L is the current revision.
MIL-PRF-131 at a Glance
| Specification | Description |
|---|---|
| MIL-PRF-131 | Watervaporproof, greaseproof, flexible, heat-sealable barrier material. |
| MIL-PRF-131L | Current revision; supersedes MIL-PRF-131K (August 2005). |
| Class 1 | General-use material with a non-woven plastic backing. |
| Class 2 | Limited-use material with a kraft paper backing. |
| Class 3 | Specialized-use, higher-strength material with a woven scrim backing. |
| MIL-DTL-117 | Heat-sealable bags made from specified barrier materials, including MIL-PRF-131. |
| MIL-STD-2073-1 | Military preservation standard using MIL-PRF-131 barriers in watervaporproof Methods 41–43 and 51–53. |
Key Specifications & Characteristics
1. Watervaporproof Foil-Laminate Barrier
MIL-PRF-131 materials are designed to keep water vapor out of a sealed package. The specification limits the water vapor transmission rate (WVTR) to no more than 0.02 grams per 100 square inches per 24 hours.
Class 1 laminates commonly test well below that limit on manufacturers' data sheets.
Ordinary polyethylene bags slowly pass moisture vapor through the film. A sealed foil-laminate package blocks nearly all of it, so little outside moisture reaches the packaged item.
2. Class 1, Class 2, and Class 3 Constructions
MIL-PRF-131 establishes three classes of barrier material based on backing and intended use.
| Material Classification | Description |
|---|---|
| Class 1 (general use) | Non-woven plastic backing; intended for all packaging applications requiring a heat-sealable, flexible, watervaporproof, greaseproof barrier. |
| Class 2 (limited use) | Kraft paper backing; limited to contents of 10 pounds or less and bags whose inside length plus width does not exceed 42 inches. |
| Class 3 (specialized use) | Woven scrim backing; used where a higher-strength barrier material is required. |
Class 2 material should not be used for floating bags or double-seam junctions, and it should not be fabricated or handled below 32 °F, where the kraft backing can crack or develop pinholes.
The selected class must match the applicable military preservation method and contract requirements.
3. Heat-Sealable Construction
MIL-PRF-131 materials are designed to be heat sealed. The inner sealant layer bonds to itself under heat and pressure to close the package.
Seal integrity is essential: a wrinkle, channel, or pinhole in a seal gives moisture a path into the package.
Material should be sealed at the settings recommended for that material and verified on the sealing equipment in use.
4. Strength and Puncture Resistance
MIL-PRF-131 sets minimum mechanical performance for the barrier material, including breaking strength and puncture resistance. Under the current revision, Class 1 material must resist a puncture force of at least 15 pounds.
Sharp edges and projections on packaged items should still be cushioned or padded, because a single puncture defeats the moisture barrier.
5. Greaseproof Performance
MIL-PRF-131 materials are greaseproof, so oils, lubricants, and preservative compounds applied to an item do not migrate through the barrier.
This makes the material suitable for items packed with preservative coatings.
6. Testing, Identification, and Quality Control
MIL-PRF-131 uses test procedures from MIL-STD-3010, Test Procedures for Packaging Materials and Containers, to evaluate properties such as water vapor transmission, strength, and sealing.
Marking provisions address information such as the specification designation, class, manufacturer, and date of manufacture, so that material can be identified after it is cut from the roll.
Additional shipment and storage markings may be required under MIL-STD-129, depending on the contract.
7. MIL-DTL-117 Bag Configurations
Finished bags made from MIL-PRF-131 material are specified under MIL-DTL-117, which identifies bags by type, class, and style.
Bags made from MIL-PRF-131 Class 1 material are commonly called out as MIL-DTL-117, Type I, Class E, Style 1.
Using conforming barrier material alone does not automatically establish finished-bag compliance. The completed bag must also satisfy the applicable MIL-DTL-117 requirements.
8. Barrier Protection vs. Corrosion Inhibition
MIL-PRF-131 is a moisture barrier. It keeps outside water vapor from entering a sealed package, but the specification does not call for a corrosion inhibitor.
Moisture already sealed inside the package must be controlled separately, typically with activated desiccant under the Method 50 series of MIL-STD-2073-1.
Where vapor-phase corrosion inhibition is required, VCI-treated materials such as MIL-PRF-22019 or MIL-PRF-3420 may be specified, subject to MIL-STD-2073-1 compatibility requirements.
MIL-PRF-131 and MIL-STD-2073-1 Preservation Methods
MIL-STD-2073-1 establishes standardized military packaging and preservation requirements for equipment, components, and supplies.
Its Method 40 series covers watervaporproof protection, and its Method 50 series covers watervaporproof protection with desiccant. MIL-PRF-131 is the primary barrier material for both.
| Preservation Method | Application |
|---|---|
| Method 41 | Watervaporproof bag, heat sealed. |
| Method 42 | Container, watervaporproof bag, heat sealed, container. |
| Method 43 | Floating watervaporproof bag, heat sealed. |
| Method 51 | Watervaporproof bag with desiccant, heat sealed. |
| Method 52 | Container, watervaporproof bag with desiccant, heat sealed, container. |
| Method 53 | Floating watervaporproof bag with desiccant, heat sealed. |
Important: Method 50-series packs add bagged, activated desiccant conforming to MIL-D-3464, and a humidity indicator where required. Desiccant quantities, bag dimensions, and closure requirements must follow the governing preservation method and contract.
MIL-STD-2073-1 also limits the use of Class 2 material in these methods to the restrictions detailed in MIL-PRF-131.
For VCI preservation under Methods 31 and 33, see MIL-DTL-22020E VCI Bags.
Common Applications of MIL-PRF-131 Barrier Bags
Military Equipment and Defense Logistics
MIL-PRF-131 barrier bags are a standard in military preservation where moisture-sensitive items require watervaporproof packaging during storage, transportation, and distribution.
Potential applications include replacement parts, mechanical assemblies, weapon components, and other items packed under the Method 40 and 50 series.
Electronics and Sensitive Components
Circuit boards, sensors, and other components susceptible to humidity are commonly packaged in sealed foil-laminate barriers with desiccant.
Where electrostatic discharge protection is also required, MIL-PRF-81705 barrier materials may be specified instead.
Aerospace and Aviation Maintenance
Aircraft components, fittings, and spares held in storage for extended periods benefit from watervaporproof packaging that limits moisture exposure until installation.
Long-Term Storage and Export Transportation
Items stored for long periods, or shipped through humid and marine environments, face conditions that accelerate corrosion.
A sealed MIL-PRF-131 barrier with desiccant keeps outside moisture out of the package. Cushioning, seal integrity, and container selection should also be evaluated.
Firearms, Armories, and Weapon Components
Watervaporproof barrier packaging is also used for weapon components and armory spares placed in long-term storage.
Military applications must follow the applicable weapon-specific preservation instructions and contract requirements.
How Watervaporproof Packaging Prevents Corrosion
Corrosion is an electrochemical process that requires moisture at a metal surface. Humid air, condensation, and contaminants accelerate it.
A sealed MIL-PRF-131 package works by keeping water vapor out. The foil layer blocks moisture from passing through the package walls, and heat-sealed seams close the remaining paths.
Moisture already inside the package when it is sealed must be controlled separately. In Method 50-series packs, activated desiccant absorbs that moisture, and a humidity indicator can show whether the package interior has stayed dry.
Removing excess air before the final seal reduces the volume of air, and the moisture it carries, inside the package.
Effective protection still depends on proper cleaning, drying, cushioning, and seal integrity.
MIL-PRF-131 vs. Other Military Packaging Specifications
Military preservation packaging utilizes several specifications addressing different protection requirements.
| Military Specification | Primary Purpose |
|---|---|
| MIL-PRF-131 | Watervaporproof, greaseproof, flexible, heat-sealable barrier materials, typically foil laminates. |
| MIL-DTL-117 | Heat-sealable bags manufactured from specified barrier materials. |
| MIL-PRF-121 | Greaseproof, waterproof, flexible, heat-sealable barrier materials. |
| MIL-PRF-81705 | Flexible electrostatic-protective barrier materials, with additional barrier characteristics depending on type. |
| MIL-PRF-22019 / MIL-DTL-22020 | Transparent VCI-treated barrier material, and the finished VCI bags made from it. |
| MIL-PRF-22191 | Transparent, flexible, heat-sealable barrier materials. |
Each standard addresses specific material properties, packaging requirements, or protection mechanisms.
The correct selection depends on the required military preservation method, environmental exposure, and characteristics of the item being protected.
Arms Preservation Inc. MIL-PRF-131 Packaging Solutions
Arms Preservation Inc. can offer MIL-PRF-131 barrier material as finished bags or roll stock.
API supplies corrosion-prevention packaging solutions for military, industrial, aerospace, and commercial applications.
Our capabilities include evaluating requests for:
- Flat and gusseted barrier bags made from MIL-PRF-131 material
- Bags made from Class 1 film/foil/poly and Class 3 scrim/foil/poly material
- Heat-sealable MIL-PRF-131 roll stock
- Custom bag dimensions and other contract-specific packaging requirements
By combining knowledge of military preservation standards with practical packaging experience, API helps customers identify suitable moisture-barrier solutions for their intended applications.
Finished-bag conformance, material requirements, lead times, and any requested documentation are evaluated for the specific quoted configuration.
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Explore our MIL-SPEC Packaging Solutions, including Scrim/Foil/Poly Barrier Bags.
Request a MIL-PRF-131 Bag or Roll Stock Quote
Arms Preservation Inc. welcomes inquiries from military organizations, government contractors, manufacturers, distributors, and industrial customers seeking MIL-SPEC barrier packaging.
To help us evaluate your packaging requirements, please provide the following information when available:
- Applicable military specification, revision, and material class
- Bag callout (MIL-DTL-117 type, class, and style) or roll stock width and length
- Inside bag dimensions (width and length) and gusset, if any
- Estimated order quantity
- Required military preservation method
- Items being packaged
- Special marking or labeling requirements
- Certificate or documentation requirements
- Desired delivery date and shipping destination
API can review custom packaging requests and determine appropriate MIL-PRF-131 bag and roll stock options.
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Frequently Asked Questions About MIL-PRF-131
What is MIL-PRF-131?
MIL-PRF-131 is a U.S. military performance specification establishing the requirements for watervaporproof, greaseproof, flexible, heat-sealable barrier materials used in military packaging.
Can Arms Preservation Inc. supply MIL-PRF-131 bags and roll stock?
Yes. Arms Preservation Inc. can offer MIL-PRF-131 barrier material as finished bags or roll stock. Customers can submit their required dimensions, quantities, and preservation requirements for quotation.
What is the difference between MIL-PRF-131K and MIL-PRF-131L?
MIL-PRF-131L is the current revision and supersedes MIL-PRF-131K, which was issued in August 2005. Classes 1, 2, and 3 carry over. Many part numbers and solicitations still cite 131K, so quote the revision your contract names.
Is MIL-PRF-131 the same as MIL-B-131?
Yes. MIL-B-131 was the earlier designation. MIL-PRF-131J replaced MIL-B-131H in 1998 and made it a performance specification.
What is the difference between MIL-PRF-131 and MIL-DTL-117?
MIL-PRF-131 establishes requirements for the barrier material, while MIL-DTL-117 establishes requirements for the finished heat-sealable bag. Bags made from MIL-PRF-131 Class 1 material are commonly called out as MIL-DTL-117, Type I, Class E, Style 1.
What do Class 1, Class 2, and Class 3 mean?
Class 1 is general-use material with a non-woven plastic backing. Class 2 is limited-use material with a kraft paper backing, restricted to contents of 10 pounds or less. Class 3 is specialized-use, higher-strength material with a woven scrim backing.
What is the WVTR requirement for MIL-PRF-131 material?
No more than 0.02 grams of water vapor per 100 square inches per 24 hours.
Which military preservation methods use MIL-PRF-131 bags?
MIL-STD-2073-1 uses MIL-PRF-131 barriers in its watervaporproof methods: Methods 41, 42, and 43, and Methods 51, 52, and 53, which add desiccant.
Do MIL-PRF-131 bags require desiccant?
It depends on the preservation method. Method 50-series packs add bagged, activated desiccant conforming to MIL-D-3464; Method 40-series packs do not. Desiccant requirements should not be changed contrary to the governing instructions.
Do MIL-PRF-131 bags prevent corrosion on their own?
MIL-PRF-131 is a moisture barrier, not a corrosion inhibitor. Protection also depends on a clean, dry item, desiccant where the method requires it, and preservatives or VCI materials where specified.
Do MIL-PRF-131 bags need to be heat sealed?
Yes, for military preservation. Methods 41 through 43 and 51 through 53 call for heat-sealed packs. A reclosable closure is a storage convenience and should not be substituted for a specified heat seal.
Can API provide custom MIL-PRF-131 bag sizes?
API can review custom MIL-PRF-131 packaging requirements, including bags in customer-specified dimensions and roll stock. Availability, manufacturing requirements, and lead times are confirmed during quotation.
How do I request a MIL-PRF-131 quote?
Contact Arms Preservation Inc. with the applicable specification, material class, bag configuration or roll stock size, estimated quantity, preservation method, and delivery requirements. API can then evaluate appropriate options.
Military Specification References
For additional information, consult the applicable official military specifications and preservation standards:
- MIL-PRF-131: Barrier Materials, Watervaporproof, Greaseproof, Flexible, Heat-Sealable.
- MIL-DTL-117: Bags, Heat-Sealable.
- MIL-STD-2073-1: Standard Practice for Military Packaging.
- MIL-D-3464: Desiccants, Activated, Bagged, Packaging Use and Static Dehumidification.
- MIL-STD-3010: Test Procedures for Packaging Materials and Containers.
Current military specification revisions and associated requirements can be reviewed through the Defense Logistics Agency ASSIST QuickSearch database.
Military-Grade Moisture Protection Starts with the Right Barrier
Reliable moisture protection requires more than placing an item inside a foil bag. Barrier material, seal integrity, desiccant, cushioning, and the governing preservation method all contribute to successful preservation.
Arms Preservation Inc. can offer MIL-PRF-131 barrier material as finished bags or roll stock, along with related preservation packaging solutions for military, aerospace, and industrial applications.
Whether you require custom barrier bags, roll stock for in-house fabrication, or assistance evaluating military preservation requirements, API welcomes the opportunity to discuss your project.
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Arms Preservation Inc. | CAGE Code: 99BK6 | Proudly Made in the USA
Technical information is provided for general reference. MIL-PRF-131 conformance applies to the specific material and packaging configuration supplied under the applicable order requirements and does not imply that all Arms Preservation Inc. products meet this specification. Contract documents and current military specifications govern.
