One of the most common questions buyers ask is: Are Mylar bags waterproof? The short answer is: Yes, when manufactured and sealed correctly, Mylar bags are highly waterproof and moisture resistant.

When it comes to storing food, supplements, cannabis products, or retail goods, moisture can ruin your products. 

In this article we will look at what this means for you, and how it impacts your business, and the there are guidelines to adhere to.

What Are Mylar Bags Made Of?

Multiple laminated layers are usually used to create Mylar bags. Polyester film (biaxially oriented polyethylene terephthalate) (the primary layer) forms the body of the Mylar bag and is typically combined with an aluminum (foil) layer, and the inner sealant layer (food-safe). 

Each of the layers has a different function: the polyester layer provides strength and prevents puncture; the aluminum layer prevents the entry of light, oxygen, and moisture; and the inner sealant layer allows you to create a heat seal shut. When combined, these layers create a very strong moisture barrier.

Mylar bags are watertight by nature. There are no properties of this material that make it structurally sound to absorb liquids; hence fluids cannot penetrate through or vapors will leak through.

Are Mylar Bags Truly Waterproof?

Yes, Mylar bags themselves are waterproof. The material does not absorb water, and liquid cannot pass through the film. Moisture cannot penetrate the bag walls under normal conditions.

How well a Mylar bag will resist moisture will depend on two very critical factors:

(1) Integrity of the bag - there are no pinholes or defects in the manufacturing process
(2) How well the bag has been sealed - using heat sealing or a quality seal.

If there is no seal, or if the seal is of poor quality, there is an opportunity for moisture to seep into the Mylar bag, though the material itself is waterproof.

Waterproof vs Airtight: What Is the Difference?

A lot of individuals mix up waterproof with completely sealed off from air. Though Mylar bags are very good at these two features, waterproof is not the same thing as airtight.

When we say a Mylar bag is waterproof, it means that liquid water can't get through the vinyl bag. When we say a Mylar bag is airtight, we mean that gas such as oxygen or humidity can't get through either. When Mylar bags are sealed correctly, they create a high-quality seal that allows both features to work exactly like they should; this is why they are commonly used for extended periods of time in food storage and for products sold in retail stores that require extra protection.

Do Zipper Mylar Bags Stay Waterproof?

Zipper resealable Mylar bags can be very useful; however, the ability to be waterproof is limited compared to a heat sealed zipper bag. Zippered bags tend to resist moisture fairly well through everyday use, but may not be completely waterproof when submerged or exposed to long-term high humidity.

Many bag manufacturers will use a zipper for daily access and heat seal the bag after the zipper for shipping and/or long-term storage to provide the best level of waterproof protection.

When Waterproof Mylar Bags Matter Most

Mylar bags are particularly advantageous in circumstances like:

• Food storage with moisture causing spoilage or mold
• Cannabis/hemp packaging, whereby humidity affects freshness
• Supplements/powders that clump due to moisture exposure
• Outdoor, emergency or long-term storage environments
• Shipping goods in humid or wet areas.

When it comes to these specific applications, the barrier properties of Mylar are far superior to other materials such as paper, cardboard and a broad range of plastics.

Why Brands Are Switching to Waterproof Custom Mylar Bags

More companies are choosing to not use traditional packaging, but instead use waterproof custom Mylar bags because they can protect the product and therefore increase profits. When water gets into a package, it will cause product damage and a higher number of product returns to the store, while making consumers lose trust in the brand quickly.

By using waterproof custom Mylar bags, companies can protect their product's freshness/shelf life, presentation, and get to sell more of it all at the same time. The laminated barrier construction/structure prevents water from getting into the bag, as well as keeping the bag durable throughout the shipping and storage/retail experience. This type of bag is especially important for products manufactured in different regions with varying climates; products that can take a very long time to be shelved will benefit greatly as well.

So, Are Mylar Bags Waterproof?