Although the name suggests otherwise, most Mylar bags are not fully composed of just the material Mylar, but are multi-layered laminations, with an outer layer made of Mylar while other layers serve various functions.

These layers include:

- Strength and heat resistant layer (Mylar)
- Oxygen, moisture, and light blocking (Aluminum foil)
- Food safe (polyethylene) for inside of package for safe product contact

By using these layers in a fusion formation, you can achieve a flexible but extremely durable barrier which far surpasses traditional plastic bag increasing their effectiveness by many times.

How Mylar Bags Protect What’s Inside

Mylar bags help to combat four major product freshness threats at the same time.

1. Oxygen Barrier

Oxygen is responsible for oxidizing food and will therefore cause it to become stale, less potent, smell bad, and have a shorter shelf life.

Mylar's internal aluminum foil layer acts as an oxygen barrier; it has such a low oxygen transmission rate that oxygen cannot easily pass through the Mylar.

That is why Mylar bag storage often uses oxygen absorbers for extended-term preservation.

2. Moisture Control

Humidity is another major threat to freshness. Moisture will promote the growth of mold; cause food or other items to clump together; change the texture of food or other items; and foster bacterial growth.

When sealed correctly, Mylar bags create a vapor barrier that inhibits the transfer of moisture to near-zero.

For this reason, Mylar bags are commonly used to store dry foods, powders, and hygroscopic materials.

3. Light Protection

Light, especially ultraviolet light, will cause the deterioration of food, supplements, herbs, or chemicals over time.

Mylar's opaque construction as well as its aluminum foil lining gives it complete light-blocking capability, which prevents photo-degradation and preserves the appearance, taste, and efficacy of an item.

4. Physical Durability

Unlike plastic, Mylar is resistant to ripping and tearing.

The durability of Mylar is extremely important during the shipping process as well as during the stacking, handling, and long-term storage process. A single area where Mylar sealing fails will ruin the product stored inside; therefore, Mylar's sealing ability creates a point of safety against loss due to seal failure.

How Heat Sealing Makes Mylar Bags Work Even Better

When a Mylar bag isn't sealed properly, it won't perform its job. 

Heat-sealing a mylar bag is the process through which both sides of the bag get fused together under the right amount of heat for a sufficient amount of time through the melting of the inner polyethylene layer to form an airtight seam. 

Once sealed:
- There is no air that can get into the bag.
- There is no moisture that can seep into the bag.
- There will be minimal oxygen exchange. 

Zipper-type Mylar bags, too, will benefit from heat sealing above the zipper, because a heat seal is what keeps the barrier of the bag intact. 

A zipper type of closure is for ease; a heat seal locks the barrier in place for the duration of the bag's use.

Do Mylar Bags Work Without Oxygen Absorbers?

Certainly, but within limits.

A mylar bag that is sealed will slow the exposure of oxygen to your product, however it will not extract the oxygen from the environment that is trapped in the bag.
 
Oxygen absorbers will actively eliminate oxygen from the sealed environment so that a low oxygen level is created therefore allowing a longer shelf life for your product.

For short term storage the mylar bag will be fine on it’s own, for long term storage the combination of a mylar bag plus oxygen absorbers is the absolute best way to store food.

Why Mylar Bags Are Used Across So Many Industries

Mylar bags function so well that they are now the standard across many industries. 

Mylar bags are being utilized to store: 

* Food and meal preparation.
* Coffee and tea.
* Nutritional supplements and nutraceuticals.
* Cannabis and hemp products.
* Pet food and treats.
* Emergency situations. 

This level of protection for the product being packaged is very useful (there is not a lot of material that can provide this). Mylar bags are light, flexible, and inexpensive.

Do Custom Mylar Pouches Work the Same Way?

Indeed, a correctly made custom Mylar pouch works. Custom-made Mylar pouch bags have the same barrier properties as normal Mylar bags; however, they are branded differently and have different sizes, finishes, and extra details such as zippers, tear notches, valves, or child-resistant closure options.

Custom Mylar pouches will perform as well as regular Mylar bags based on their laminate structure and sealing quality. However, they may perform better than regular Mylar bags because they are typically made from thicker films or upgraded materials.

Understanding how Mylar bags work also explains why custom Mylar pouches are commonly used in commercial packaging, where consistency and barrier performance matter more than appearance alone.

So, How Do Mylar Bags Work?

Mylar bags work by using a layered barrier of polyester film, aluminum foil, and food safe plastic to block oxygen, moisture, light, and contaminants. When heat sealed, they create an airtight environment that slows oxidation and preserves freshness.

Final Thoughts

The way in which mylar bags function is to merge multiple levels of defense together in a sealed barrier constructed to stop oxygen, moisture, light, and damage simultaneously. 

This is where the magic occurs.

They are not magically-attributed; rather, they act as man-made barriers engineered to delay the effects of nature that cause products to deteriorate with time.

If mylar bags are properly sealed and utilized for the appropriate application, they continue to be some of the best storage and packaging solutions available.