If you’ve ever wondered how to seal ziplock Mylar bags the right way, you’re not alone.

To seal a ziplock Mylar bag: Close the ziplock first, press out as much air as possible, then use a heat source like a impulse sealer or hair straightener to seal the top above the zipper. This creates a fully airtight seal for long-term storage.

When sealing Ziplock Mylar bags, the primary goal isn't just to zip the bag shut. It is to have a complete level of protection (we're talking long-term protection for your food, food herbs, medicines, or any very sensitive items) by creating a multi-layered barrier against moisture, air, and contaminants that will last the life of the items safe from spoiling. Additionally, using a heat seal ensures that items will not spoil... it creates an actual vault-like barrier once sealed.

This is a guide on how to properly seal Ziplock Mylar bags, including what tools to use and tricks to avoid making small mistakes that may slowly ruin the long-term storage life of stored items.

Quick Answer

To seal a ziplock Mylar Bag:

• Close the ziplock tightly to create an initial seal
• Press out as much air as possible from the bag
• Place a heat source (flat iron or heat sealer) above the zipper
• Clamp and hold for 2 to 4 seconds across the top
• Check for a smooth, fully sealed line with no gaps

Why Ziplock Alone May Not Be Enough

Most Ziplock Mylar bags have a resealable zipper for convenience, but this zipper will not create a full-fledged vacuum seal like they claim. Here is the simple truth....

Zippers are designed for short-term access

Air and oxygen (as well as moisture) have numerous small entry points, allowing for air and moisture to slowly make their way into the bag.

If you are storing anything of value or perishable, you must also heat seal above the zipper to seal everything in permanently.

Tools for Seal Online

You will not need a bunch of fancy tools to help you seal, just enough that you can produce a uniform heat.

Best options:

• Impulse heat sealer (this is the best tool for sealing mylar bags)
• Hair straightener
• Ironing cloth

How To Seal Ziplock Mylar Bags - Step-by-Step

Seal the zipper closed, remove excess air, then apply heat across the top edge above the zip using a flat iron or heat sealer until a smooth seal forms, locking out air and moisture.

1) Fill Bag Properly

Leave 1 to 2 inches of space from the top of the bag. Overfilling a ziplock Mylar bag is one of the simplest methods to create a faulty seal.

If you're storing food or anything for the long term:

• Place the proper size oxygen absorber in the bag.
• Work quickly, as they immediately begin absorbing oxygen.

2) Press the Ziplock Closed

You can make a temporary seal by using your fingers to run along the zipper and:

• Push out any excess air
• Create a temporary seal

This will secure the bag in place before heat sealing.

3) Remove Remaining Air

To remove remaining air and improve your results:

• Gently squeeze the bag to remove remaining air, or
• Use a straw to suck any excess air out

The less air in the bag, the longer the shelf life will be. For best results, press the bag gently, or use a straw to get out as much air as possible. For more info on methods to remove air from Mylar bags please refer to our guide.

4) Heat Seal Above the Zipper

This step is the most critical one in sealing the bag.

• Using a hair straightener or a heat sealer, clamp an area above the zipper track
• Hold the clamped area for two to four seconds.
• Move across the width of the bag evenly until the entire top area has been sealed.

You should have a seal that appears smooth and slightly shiny.

5) Test Your Seals

Lightly squeeze the bag:

• You should not feel or see any air escaping from the bag.
• The seals should have a uniform appearance (i.e., not wrinkled or patchy).

If the seal appears questionable, reseal the bag higher above the previous seal.

Common Mistakes to Avoid

Even minor mistakes can result in a faulty seal.

Common mistakes include:

• Sealing the bag too low and melting the zipper area.
• Not applying enough heat and providing weak seals.
• Applying too much heat and burning through the bag.
• Product or dust in the area where the seal is applied to the bag.
• Overfilling the bag and not being able to seal properly.

Any of these mistakes will create one faulty seal, rendering your "air-tight" bag as if it has a nail in it and is leaking like a tire with a nail in it.

Can You Reseal A Ziplock Mylar Bag?

Yes, but only if you left extra space in the bag above the previous seal.

To reseal:

• Cut below the pre-existing seal.
• Zip the bag closed.
• Heat seal again above the new zipper seal (optional)

You will run out of usable material at the top of the bag after a few reseals.

When to Use Professional Sealing

If you need to seal large volumes of product or if you are selling your products, you will find an impulse sealer gives you consistent results, cleaner seals which result in better product presentation and faster workflow which saves you time.

Your seal is an important part of your product experience, especially for branded products.

Why Custom Mylar Bags Matter

If you are using custom Mylar bags to sell your products, the sealing process is directly related to the quality of your packaging.

High quality custom mylar packaging bags will:

• Provide more consistent seals
• Have stronger barrier layers
• Maintain structural integrity under heat

That's why brands looking to scale use professionally made packaging through Brandmydispo as their material and seal quality has been tested for real-world use.

Final Thoughts

To seal ziplock mylar bags, press the ziplock shut, push out remaining air, then run a heat sealer or flat iron across the top section above the zipper to create a tight, permanent seal that keeps contents fresh.

While sealing a ziplock Mylar bag properly can be easy, it can also be unforgiving (i.e., if you skip a step, rush the heat sealing process or don't trust the zipper seal on it's own). You will be taking a big risk with whatever is inside the bag.

However, if you follow these simple steps, once sealed you will have essentially created a time capsule. No air will be able to get in, your freshness will be preserved and nothing from the outside will be able to get inside the bag.