How to Seal Mylar Bags (Without Buying a Sealer) (2026)

The tool you already own

A flat iron is close to purpose-built for this. It applies even heat from both sides and clamps with steady pressure, which is precisely what fusing two layers of Mylar requires, and it costs nothing if there is one in the house already:

When sealing mylar bags I always use a hair straightener. Turn it up to its highest temp and seal the edge of the bag. It is much less cumbersome then using an iron. And much less expensive then a mylar bag heat sealer.

A clothes iron is the other household answer, and plenty of people get years out of it, with the most convincing kind of evidence behind them, which is bags opened long after sealing:

The easiest way to seal a mylar bag is using a regular clothes iron, set at "wool" (a fairly high temperature). I've opened bags of cereal that were bagged in 2014 and crackers that were bagged in 2013, and both were fine.

We would still put it second, and it is worth knowing why. The one organisation that packs Mylar pouches at institutional scale tells its members not to use an iron or other household heating device, on the grounds that it will not give an adequate seal, and it singles out powders like flour and dry milk as where that fails first. The mechanism fits: an iron heats from one side and you supply the pressure by hand, so dwell and force vary along the seam in a way a clamp does not. Use one on thinner bags of granular food if it is what you have, check the seam carefully, and prefer a flat iron or a real sealer for powders and thick bags.

The mistake: heat without pressure

This is the single most useful thing to understand, and it explains why people who own perfectly hot tools still get failed seals. Melting the inner layer is only half the job. The two faces have to be pressed together while that layer is molten, and then held still while it cools, or they simply do not fuse:

A heat gun will easily hit the required temperature, but you're not sealing anything without applying pressure to it.

So a heat gun, a lighter, or waving an iron over the bag will all get the material hot and none of them will seal it. A heat gun is doubly wrong, because it runs far hotter than the polyester outer layer can survive, so it wrecks the barrier before the inner layer bonds. Clamp, or press against something solid. That is also why a flat iron beats a clothes iron for most people: the clamping is built in and the pressure stays even. Firm and even is the target, not hard, since squeezing too aggressively pushes the molten layer out of the seam and thins the very thing you are building.

Settings and timing that actually work

There is no universal number, because output varies by device, but the range owners converge on is a high setting held for several seconds per section, moving slowly rather than sweeping:

I used a Conair ceramic flat iron. Setting 15 of 25. Gets quite hot at that setting, actually. I would hold it for about 5 seconds and slowly move it across the top to get a wide seal.

Two details in there are worth copying. Five seconds per section is far longer than instinct suggests, and moving slowly to build a wide seam is better than a fast pass that leaves a thin line. A wide, fully fused band is what survives years of handling. If your bags are thicker, expect to hold longer, which is covered in our Mylar bag thickness guide.

Why a bathroom tool can do this at all

It is worth knowing what is actually melting, because it explains both why this works and how you can ruin a bag. A Mylar food bag is a laminate: a polyester and foil outer structure for the barrier, and a polyethylene inner layer that faces the food. Polyethylene melts at roughly 210 to 260F, while the polyester side does not melt until close to 490F. A flat iron lands in that gap, so it fuses the two inner faces together without touching the barrier layers.

That gap is also your safety margin in both directions. Household tools cannot get near the temperatures at which these films actually break down, which is why sealing a bag is not a fumes problem the way industrial plastic processing can be. What a household tool can absolutely do is melt straight through the bag if you park it in one spot, so keep it moving and stop the moment the seam looks glossy and flat rather than wrinkled.

Seal above the zipper, not on it

Many Mylar bags ship with a ziplock strip, and it is a convenience feature rather than a storage seal. The heat seal is what holds for years:

you should heat seal above the zip seal. The zip is not as airtight.

The practical trick that follows is to leave a gap between the zipper and your heat seal. When you eventually open the bag, cut below the heat seam and above the zipper, and you still have a working ziplock to close the bag while you use up the contents. It costs nothing and makes the bag reusable in the short term.

Test the seal before you trust it

Do not assume the seam took. Whether it holds depends on the tool, the bag, and how long you held it, and none of that is guaranteed by following instructions:

there's no guarantee - need to test - depends on hair straitner quality (amperage) - mil thickness of the mylar - age of the device

A quick check on every bag:

• Let the seam cool fully before you touch it, since a warm seal is weak and peels apart easily.
• Rub the seal between thumb and forefinger, feeling for folds, ridges, or wrinkles. Those channels are the classic long-term failure, and a tug will not find them.
• Look for food caught in the seam. No product should be visible in the seal band, and a single grain or a dusting of flour is enough to open a leak path.
• Aim for a seal band at least a sixteenth of an inch wide, and pull the bag flat before you press so you are not sealing a wrinkle in.
• Tug the two sides apart firmly. This catches gross failures only; a good seal does not separate at all.
• If in doubt, run a second seam at a different height rather than re-ironing the first, since re-melting a finished seal degrades it.
• Check again over the next few days. A working absorber pulls the sides in, more visibly on grains than on powders.

That last check is the most useful one you have, and it is worth knowing what to expect. The bag firms up over a day or several rather than overnight, and it does not shrink-wrap tight, because the absorber only takes the oxygen and leaves the nitrogen behind. Read it in one direction only: sides drawn in is good evidence the seal holds, but a bag that has not visibly pulled in is not proof of failure, since powders show it far less and the absorber may simply be undersized.

When to just buy the sealer

The household-tool route is genuinely fine for a few dozen bags. Past that, or with thick bags, the case for a real impulse sealer gets strong, and it is cheaper than people assume:

I just buy cheap impulse sealer on ebay. Works better, timer and heat settings are better than guess work

That names the actual advantage, which is repeatability rather than raw heat. A timer means every seam gets the same dwell, so you are not judging by feel on bag forty as your hand gets tired. A 12-inch bar also closes most of a bag in one press rather than three overlapping passes, which removes the likeliest place for a gap to hide.

Two practical notes on the household route. Melted residue does end up on the plates, so use an old flat iron or a cheap dedicated one rather than someone's good styling tool, and wipe it cold rather than burning residue off. And it is worth saying plainly that the household-appliance method is community practice rather than institutional advice: extension services and the large-scale packers describe the pouches and then specify a proper sealer. It works, people have decades-old bags to show for it, and it is still the improvised route rather than the endorsed one.

Two safety points before you start

Seal only genuinely dry food. This is the one that actually matters. An oxygen absorber in a sealed bag creates exactly the low-oxygen environment Clostridium botulinum prefers, so anything with meaningful moisture in it does not belong in there at room temperature. Dry staples at roughly ten percent moisture or less are the target: rice, beans, wheat, pasta, oats, flour. Anything moist, low-acid, or home-dried but not crisp-dry goes in the fridge or freezer instead. Our guide to what should never go in Mylar covers the sorting.

Treat the hot tool like the burn hazard it is. Flat-iron plates run hot enough to burn skin on contact in about a second, and hair straighteners are a well-documented cause of serious burns in small children. Two details catch people out: the plates stay dangerous for up to forty minutes after you switch off, and a good share of those injuries happen with the device already off, so park it somewhere out of reach rather than on the counter to cool. Route the cord away from the counter edge, since cord-pulls are their own category of burn. Work on stone or a silicone mat rather than a laminate worktop or a towel, and do not leave it plugged in unattended.

The whole process, start to finish

Put it together and sealing a bucket of rice takes a couple of minutes. Line the bucket with the Mylar bag, fill it and leave a few inches of headroom, drop in the correctly sized oxygen absorber, and press the loose air out by hand. Lay the top of the bag flat, seal above the zipper with a flat iron on high, holding about five seconds per section and overlapping your passes. Let it cool, tug-test the seam, add a second seal if it feels marginal, then snap the bucket lid on and label it.

For the absorber sizing, see our oxygen absorber guide, and for why the bucket goes around the bag rather than replacing it, our bucket vs Mylar guide covers the division of labour.