You need a heat sealer with a jaw wide enough to cross the bag in one pass. A 12-inch impulse sealer handles gallon mylar in a single 1.5-second press. Most seal failures come from one of three things: a narrow sealer used in two passes, food caught in the seal line, or not checking afterwards.
What kind of sealer
| Type | Handles 7 mil? | Verdict |
|---|---|---|
| Impulse sealer, 12 in | Yes, one pass | The right tool. What we use |
| Impulse sealer, 8 in | Yes, two passes on a gallon bag | Workable but the overlap is a weak point |
| Household iron | Marginally | Hard to control temperature; inconsistent |
| Hair straightener | 3.5 mil only | Will not seal 7 mil reliably. Do not trust a store to it |
| Vacuum sealer | No | Wrong tool – designed for thin vacuum bags, not mylar |
The technique
- Fill, leaving headroom. Two to three inches of empty bag above the food. You need clean film to seal, and food in the seal line is the second most common failure.
- Drop the absorber in last, on top of the food, and move straight to sealing. Do not fill ten bags and then start adding absorbers.
- Press the air out gently. Do not try to vacuum it — the absorber handles the oxygen. You are just reducing bulk.
- Seal in one pass. Hold for the full dwell time, usually one to two seconds on 7 mil, then let the jaw cool a moment before lifting.
- Check it. Run a finger along the seal feeling for gaps, then squeeze the bag firmly. Any hiss means reseal.
- Label it with contents and date. Ideally before you filled it.
The three failures
- Two-pass overlap. Where two seal passes meet there is a short section that was heated twice and a tiny gap where they do not quite align. This is where narrow sealers fail. Overlap generously if you must do two passes.
- Food or powder in the seal. A single crumb of freeze-dried powder in the seal line creates a channel. Wipe the inside of the bag mouth before sealing if you have been working with anything dusty.
- Not letting it cool. An impulse sealer heats a wire and then stops. If you lift the jaw immediately the molten seal can pull apart. Count to two before releasing.
Do you need a vacuum sealer as well?
Not for mylar storage, no. The oxygen absorber removes the oxygen far more completely than a vacuum sealer can, and pulling a vacuum on mylar can crush brittle food and stress the seams. A vacuum sealer is useful for short-term fridge and freezer storage in its own bags, which is a different job.
If you already own one, keep it for that. If you are choosing between the two for freeze-dried storage, buy the impulse sealer.
Impulse heat sealer, 12 in
Twelve-inch jaw crosses a gallon bag in one pass, which removes the most common cause of seal failure. Verified 6 September 2026.