Packaging Guides
How to Seal Mylar Bags: Heat Sealer, Impulse Sealer & Iron Guide (2026)
Cubit Packaging
April 8, 2026
Quick Answer: Sealing mylar bags requires heat between 375°F–420°F (190°C–215°C) applied to the bag opening to fuse the polyethylene inner lining. An impulse sealer provides the most consistent results with less than 0.5% failure rate, though a household iron on the "wool" setting or a hair straightener works for small batches. Always add oxygen absorbers before sealing for long-term storage.
What You Need Before Sealing
Before sealing any mylar bag, gather these essential supplies: mylar bags (5 mil+ for long-term storage), a heat source (impulse sealer, iron, or flat iron), oxygen absorbers (300–500cc per gallon of product), a flat surface, and a permanent marker for labeling every bag with date and contents.
Flat mylar bags ready for heat sealing — ideal for food storage and product packaging
Pro Tip from Cubit Packaging: For commercial operations sealing 50+ bags daily, invest in a 12" or 16" impulse sealer with adjustable heat and timer settings. The consistency pays for itself within the first production run.
Method 1: Impulse Sealer (Recommended)
An impulse sealer is an electrically heated device that applies a precise burst of heat to create a uniform seal across the bag opening. It is the preferred method for commercial packaging because it delivers consistent, repeatable results with a seal failure rate of less than 0.5% compared to 3–5% for manual iron sealing (Flexible Packaging Association, 2025).
Step-by-Step Instructions
- Set the temperature to 375°F–420°F (or heat setting 5–7 on most impulse sealers)
- Fill the bag with your product, leaving 2–3 inches of empty space at the top
- Insert oxygen absorbers if applicable
- Squeeze out excess air by pressing firmly on the bag from bottom to top
- Place the bag opening between the sealer jaws — ensure material lies flat with no wrinkles
- Press the sealer handle down firmly and hold for 2–4 seconds
- Wait for the cooling cycle (most impulse sealers beep when complete)
- Inspect the seal — a proper seal is smooth, uniform, and cannot be pulled apart by hand
Temperature Reference Chart
| Bag Thickness | Temperature Range | Seal Time | Notes |
|---|---|---|---|
| 3.5 mil | 350°F–375°F | 1.5–2 sec | Standard retail packaging |
| 5 mil | 375°F–400°F | 2–3 sec | Long-term food storage |
| 7 mil | 400°F–420°F | 3–4 sec | Heavy-duty industrial use |
| 7+ mil | 410°F–430°F | 4–5 sec | Military/emergency spec |
Method 2: Household Iron
A standard household iron is the most accessible sealing method for home users and small batch operations. Set your iron to the "Wool" or "Cotton" setting (approximately 380°F), turn OFF steam, and place a wooden ruler under the bag opening for a firm surface.
The 95% Rule
The 95% Rule is the most important technique for iron sealing: seal 95% of the bag opening first, then use the remaining 5% gap to squeeze out trapped air before completing the final seal. This method reduces oxygen exposure by up to 90% compared to sealing all at once.
Kraft mylar bags sealed with heat sealing method — natural eco-friendly look with mylar barrier protection
Method 3: Flat Iron / Hair Straightener
A hair straightener works well for small mylar bags under 6 inches wide. Set to 380°F–400°F, clamp over the bag opening, and slowly draw across at 1 inch per second. Best for sample bags, party favors, and testing seal quality before scaling up.
Oxygen Absorber Guide
Oxygen absorbers (OAs) are iron powder packets that chemically react with and remove oxygen inside a sealed container. For mylar bags used in food storage, they are essential — reducing internal oxygen from 21% to below 0.01%, preventing oxidation, mold growth, and insect survival.
How Many Oxygen Absorbers Per Bag?
| Bag Size | Dense Products (rice, beans) | Loose Products (pasta, cereal) |
|---|---|---|
| 1 quart (6×9") | 100–200cc | 200–300cc |
| 1 gallon (10×14") | 300–500cc | 500–800cc |
| 5 gallon (18×28") | 1,500–2,000cc | 2,000–3,000cc |
"Properly sealed 5-mil mylar bags with appropriate oxygen absorbers can preserve white rice for 25+ years, wheat berries for 30+ years, and dried beans for 20+ years when stored at 50°F–70°F in dark, dry conditions" — Utah State University Extension, 2024.
Which Foods Can You Store in Mylar Bags?
| ✅ Excellent for Mylar | Shelf Life | ❌ Not Recommended | Reason |
|---|---|---|---|
| White rice | 25+ years | Nuts | High oil content |
| Dried beans | 20+ years | Brown rice | Oils go rancid |
| Wheat berries | 30+ years | Fresh produce | Too much moisture |
| Rolled oats | 20+ years | Meat (unless freeze-dried) | Moisture + fat |
| Dried pasta | 20+ years | Chocolate | Melts, high oil |
| Coffee beans | 2–3 years | Liquids | Not designed for liquid |
| Sugar | Indefinite | Fermented foods | Gas production |
Sealing Equipment Comparison
| Feature | Impulse Sealer | Household Iron | Flat Iron |
|---|---|---|---|
| Consistency | ⭐⭐⭐⭐⭐ | ⭐⭐⭐ | ⭐⭐⭐ |
| Speed | 2–4 sec/bag | 5–10 sec/bag | 3–6 sec/bag |
| Max bag width | 8"–20" | Unlimited | 1"–6" |
| Best for | Commercial use | Home storage | Small bags |
| Cost | $35–$200 | Already own | Already own |
| Failure rate | <0.5% | 3–5% | 2–4% |
Common Sealing Mistakes
Mistake 1: Wrinkled Seals
Folds or wrinkles create micro-channels for oxygen entry. Fix: Smooth the bag opening flat and hold the material taut with both hands before sealing.
Mistake 2: Wrong Temperature
Too low = weak seal that peels. Too high = melted, brittle bag. Fix: Test on scrap first. Start at 375°F and increase in 10° increments.
Mistake 3: Skipping Oxygen Absorbers
A sealed bag without OAs still contains 21% oxygen. Fix: Use the chart above to calculate correct OA size.
Mistake 4: Sealing Moist Products
Moisture inside a sealed mylar bag creates conditions for botulism and mold. Fix: Only seal products with less than 10% moisture content.
Custom printed mylar bags with professional branding — fully sealed and retail-ready
Frequently Asked Questions
What temperature do you seal mylar bags at?
Mylar bags seal best at 375°F to 420°F (190°C to 215°C). The exact temperature depends on bag thickness — 3.5 mil bags need 350°F–375°F, while 5+ mil bags require 375°F–420°F. Always test on a small area first and adjust based on results.
Can you seal mylar bags with a regular iron?
Yes, a household iron set to the "Wool" or "Cotton" setting (approximately 380°F) can effectively seal mylar bags. Turn off steam, place the bag on a hard flat surface with a wooden board underneath, and press firmly for 3–5 seconds. Use the 95% rule: seal most of the opening first, push out air, then finish.
Do you need oxygen absorbers in mylar bags?
For long-term food storage (1+ years), oxygen absorbers are essential. A sealed mylar bag without them still contains 21% oxygen — enough for mold and insect eggs to hatch. Use 300–500cc per gallon for dense foods, 500–800cc for loose foods.
How long do mylar bags keep food fresh?
Properly sealed mylar bags with oxygen absorbers preserve low-moisture foods for 20–30+ years. White rice lasts 25+ years, wheat berries 30+ years, dried beans 20+ years. Store at 50°F–70°F in dark, dry conditions for maximum longevity.
What is the best mylar bag thickness for food storage?
For long-term emergency food storage, use 5 mil or thicker. While 3.5 mil works for retail packaging (1–2 years), 5–7 mil bags provide superior puncture resistance and long-term barrier protection. Cubit Packaging offers bags from 3.5 mil to 7+ mil.
Can you vacuum seal mylar bags?
Mylar bags are not ideal for vacuum sealing because the rigid material does not collapse uniformly. Use the squeeze-and-seal method with oxygen absorbers instead. For a detailed comparison, see our guide on Mylar Bags vs Vacuum Seal.
What is the correct mylar bag sealing temperature?
The correct mylar bag sealing temperature is 375°F to 420°F (190°C to 215°C) for impulse sealers, or medium-high heat (wool/cotton setting, approximately 380°F) for household irons and hair straighteners. Thinner bags (3.5 mil) seal at the lower end (350°F–375°F), while thicker bags (5–7 mil) require the higher end (400°F–420°F). If the seal wrinkles or burns, reduce the temperature by 10°F increments.
Do mylar bags need to be heat sealed?
Yes, mylar bags must be heat sealed to create an airtight barrier. Unlike vacuum seal bags or ziplock bags, mylar's polyethylene inner layer requires heat fusion at 375°F+ to bond. Ziplock closures on mylar bags provide re-sealability but are not airtight on their own — you still need a heat seal across the top for long-term storage. The only exception is mylar bags with adhesive strip closures, but these have a significantly shorter shelf life (6–12 months vs 20–30 years with heat sealing).
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