Heat shrink wrapping and vapor barrier bags are both used to keep moisture away from equipment, and they work in opposite directions. Shrink film keeps weather out, which also means it keeps whatever is already inside, inside. A vapor barrier bag creates a sealed low humidity environment using desiccant to control the moisture that was trapped at seal time. Confusing the two, or using the first while assuming it does the job of the second, is how equipment arrives corroded inside intact packaging. Here is what each one actually does and how to specify them.
We apply both at our Las Vegas facility and at client sites, on everything from casino equipment and machinery to export freight. If you need a crate built around something that cannot move, see our post on on-site crating instead.
Shrink Wrap Is Not Stretch Wrap
Worth clearing up first, because the terms get used interchangeably and they are different products doing different jobs.
- Stretch wrap is a thin film pulled tight by tension, usually machine or hand applied around a palletised load. It holds a stack together. It is not weatherproof and is not intended to be.
- Shrink wrap is a thicker film applied loosely and then heated so it contracts to the shape of the object. It forms a taut, sealed skin that sheds water and resists puncture, and it is what protects boats, machinery and outdoor stored equipment.
Industrial shrink film is substantially heavier than the retail film most people picture, and it is installed with a heat gun by someone who knows how to avoid burning through it or scorching what is underneath. It is a trade skill, not a wrapping task.
The Thing Most People Get Wrong About Shrink Wrapping
Shrink film is a moisture barrier. That is the point, and it is also the trap. Sealing an item inside a barrier encloses the air, and its moisture, that was present at the moment of sealing. As temperature cycles across day and night, that moisture condenses on the coldest surface available, which is often the equipment. The result is corrosion, mildew and staining inside packaging that looks perfect from the outside.
There are two correct answers, and which you use depends on the job:
- Ventilate. For outdoor or long term covered storage, vents are installed in the film so the enclosed space can breathe while still shedding rain and blocking dust. This is standard practice on shrink wrapped boats and stored machinery.
- Seal and desiccate. For sealed preservation you do not ventilate. You control the trapped moisture with desiccant inside a proper barrier, which is what vapor barrier bags are for.
What you should not do is seal an unvented wrap around bare metal and assume the moisture problem is solved. Anyone quoting you shrink wrapping for corrosion sensitive equipment should raise this before you do.
How Vapor Barrier Bags Work
A vapor barrier bag is a multi layer laminate, typically including a foil layer, with a very low moisture vapor transmission rate. The item is placed inside with a calculated quantity of desiccant, the bag is heat sealed, and the desiccant adsorbs the moisture that was trapped at sealing plus the small amount that migrates through the barrier over time. The result is a sealed micro environment held below the humidity at which corrosion begins.
The parts that matter when specifying one:
- Barrier material. Foil laminates give the highest moisture, oxygen and grease protection. Transparent and kraft based barriers exist for less demanding work.
- Desiccant quantity. Calculated from the bag’s interior surface area, the barrier’s transmission rate and the intended storage duration. Guessing produces either wasted desiccant or a bag that saturates and stops working halfway through storage.
- Humidity indicator card. A visible indicator inside the bag showing whether the interior has stayed dry. It converts the whole system from a hope into something inspectable without opening it.
- Seal integrity. A barrier bag is only as good as its weakest seal, and a puncture anywhere makes the desiccant calculation meaningless. Cushioning and sharp edge protection go inside the bag for this reason.
- ESD protection where required. Electronics need static dissipative barrier material, which is a different specification from a standard moisture barrier.
Which Method Does Your Item Need?
| Method | Best For | What It Does | Watch Out For |
|---|---|---|---|
| Stretch wrap | Unitising palletised loads for transit | Holds a stack together | Not weatherproof, offers no real protection |
| Vented shrink wrap | Outdoor or long term covered storage, boats, machinery | Sheds water and dust while allowing airflow | Vents must actually be installed |
| Sealed shrink wrap | Short transit, dust and handling protection | Tight protective skin, tamper evident | Traps moisture, unsuitable alone for bare metal |
| Vapor barrier bag | Corrosion sensitive metals, electronics, long storage, export | Sealed low humidity environment with desiccant | Requires correct desiccant calculation and intact seals |
| VCI materials | Metal parts, often alongside a barrier | Releases a corrosion inhibiting vapor | Material must suit the specific metal |
In practice these combine. A common industrial build is the item bagged in a vapor barrier with desiccant, cushioned, then blocked and braced inside a custom wood crate, with the whole crate shrink wrapped for the outdoor leg. Each layer solves a different problem.
Military and Defense Preservation Standards
If you are shipping to a defense contract, the packaging is specified rather than chosen. The governing document is MIL-STD-2073-1, the standard practice for military packaging, which assigns numbered methods of preservation according to the level of protection required. Methods in the 40s and 50s address water vapor proof protection, with and without desiccant, and several of them call out specific barrier materials by specification.
The specifications you will see referenced on a purchase order:
| Specification | Covers | Typical Use |
|---|---|---|
| MIL-STD-2073-1 | Standard practice for military packaging, preservation methods | Assigns the method code your contract requires |
| MIL-PRF-131 | Barrier materials: watervaporproof, greaseproof, flexible, heat sealable | Foil laminate, the high performance moisture barrier |
| MIL-DTL-117 | Bags, heat sealable | The bag itself, specified by type, class and style |
| MIL-PRF-121 | Barrier materials: greaseproof, waterproof | Kraft based barrier for lower level protection |
| MIL-PRF-81705 | Barrier materials: flexible, electrostatic protective, heat sealable | ESD bags for sensitive electronics |
| MIL-D-3464 | Desiccants, activated, bagged | The desiccant units placed inside the barrier |
If your paperwork cites a method number and a barrier specification, send them to us with the enquiry rather than describing the item. The specification determines the material, the desiccant quantity and the documentation, and building to the wrong one means the shipment fails receiving inspection. Copies of current defense specifications are available through EverySpec and the official distribution channels. Our mil spec heat shrink wrapping page covers this work.
Where These Methods Get Used
- Industrial machinery and tooling. Bare machined surfaces are the classic corrosion risk, particularly on ocean freight and long storage. See industrial shrink wrapping.
- Export freight. Ocean containers cycle through large temperature swings and generate condensation. Barrier and desiccant protection is standard on anything metallic. Wood packaging separately needs ISPM 15 heat treatment, which we stamp in house.
- Electronics and instrumentation. Static dissipative barrier material plus desiccant, often inside a cushioned crate. See electronics shipping.
- Food industry equipment. Where material compliance and cleanliness requirements apply to the wrapping itself, not only to the contents. See food industry shrink wrapping.
- Casino and entertainment assets. Signage, gaming equipment and show pieces going into storage between installs, where the enemy is months of sitting rather than miles of travel.
- Long term warehouse storage. Anything that will sit for a year or more, where the seal and the desiccant calculation matter more than the outer container.
Applying These at Your Location
Both methods can be applied on site. Shrink wrapping is well suited to it, since the equipment is portable and the film conforms to whatever it is applied to. Vapor barrier work on site needs more planning: clean conditions, a working heat sealer, and enough space to handle the barrier material without puncturing it. Heat guns also mean open flame and hot surfaces, so occupied buildings and gaming properties will have rules about hot work that need clearing in advance. Ordinary workplace safety obligations apply, including those under OSHA.
We do this work at client sites regularly as part of on-site crating and heat shrink wrapping, and the full site survey process is covered in our on-site crating guide.
Our Experience
We have been crating and packing in Las Vegas for over 25 years, including work for properties such as Wynn, Aria, Caesars, Hard Rock and Mandalay Bay, the Leonardo Da Vinci exhibit, a Formula 1 race car and the Stargate movie prop. The preservation side of the work is less photogenic than a crate around a race car, and it is where most of the avoidable damage actually happens. An item that arrives structurally perfect and internally corroded failed just as completely as one that arrived broken.
Get Your Preservation Packaging Specified
Tell us what the item is, what it is made of, where it is going, how long it will be stored, and whether a contract specifies a preservation method or barrier specification. We will come back with a recommended build and a quote. Call 702-748-4973 or 1-833-801-9084 toll free, email contact@lasvegascrating.com, or request a quote online. See our vapor barrier bags, heat shrink wrapping and crate fabrication pages.