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Mylar bags are flexible packaging pouches used across food storage, pharmaceuticals, cosmetics, and electronics. Selecting the wrong size or thickness causes two specific problems: oversized bags trap excess oxygen that accelerates spoilage, and undersized bags stress the seams and film, breaking the protective seal. This guide covers every variable you need — size by product weight and volume, thickness by storage horizon, heat-seal temperatures by mil, and shelf life by product type.
What is a Mylar bag?
A Mylar bag is a flexible pouch made from biaxially oriented polyethylene terephthalate (BoPET) film laminated with a vacuum-metallized aluminum layer and a polyethylene heat-seal inner layer. It achieves an oxygen transmission rate (OTR) below 0.01 cc/100 in²/day — classified as a high-barrier packaging material.
BoPET film — trademarked as Mylar® by DuPont Teijin Films — is produced by stretching PET polymer in two perpendicular directions during manufacture. This biaxial orientation raises tensile strength to approximately 200 MPa and elongation at break to approximately 120%, making the film resistant to puncture and tearing under storage and transit conditions.
The aluminum metallization layer, deposited at 350–450 Ångströms, blocks 99.9% of UV light and provides the primary oxygen and moisture barrier. The polyethylene inner layer melts at 140–180°C to form the heat-sealed closure. This three-layer laminate is what makes Mylar bags fundamentally different from standard PE zip bags — the barrier is in the film structure itself, not just the seal.
What are Mylar bag inner vs outer dimensions?
Mylar bag outer dimensions are the full edge-to-edge measurements including side seals, zipper height, and header space. Inner dimensions are the true usable space after subtracting sealed edges — typically 0.25–0.5 inches narrower per side. Always size your product to the inner dimension, not the label size.
A bag labeled 4″×6″ may have an inner usable width of only 3.5″ once side seals are factored in. The inner height runs from the bottom seal to the lowest point of the zipper or top seal line. When ordering custom Mylar bags at volume, always request both measurements — a bag that seems correct on paper but is 10% too tight at fill causes seal failures and product waste.
Outer dimensions matter for: fitting bags into secondary cartons, retail display fixtures, filling machine jaw widths, and hang-hole placement.
Inner dimensions matter for: actual product fill volume, oxygen absorber fit, and seal margin calculation.
What are the standard Mylar bag sizes by weight and volume?
Standard Mylar bag sizes run from 3″×5″ (0.25 qt, for spices) to 14″×20″ (5 gal, for emergency bulk storage). Size selection depends on product weight in grams or ounces, fill volume in quarts or gallons, oxygen absorber capacity, and available heat-sealer jaw width.
| Bag size (in) | Product weight equiv. | Volume approx. | O₂ absorber (cc) | Suitable for | Min. thickness | Seal jaw needed |
|---|---|---|---|---|---|---|
| 3″ × 4″ | ~1–3.5g | ~0.1 qt | 50 cc | Micro samples, single buds, small seeds | 3.5 mil | 4″ jaw |
| 3″ × 5″ | ~3.5–7g | ~0.25 qt | 50–100 cc | Spices, herbs, seed packets | 3.5 mil | 4″ jaw |
| 4″ × 6″ | ~7–14g (¼ oz) | ~0.5 qt | 100 cc | Single-serve snacks, small hardware, supplements | 3.5 mil | 6″ jaw |
| 5″ × 8″ | ~14–28g (½–1 oz) | ~1 qt | 100–150 cc | Dried fruit, nuts, coffee beans, loose-leaf tea | 4 mil | 6″ jaw |
| 6″ × 9″ | ~28g (1 oz) | ~1.5 qt | 150–200 cc | Pasta, grains, larger snack portions, coffee | 4 mil | 8″ jaw |
| 8″ × 10″ | ~113g (¼ lb) | ~2 qt | 200–300 cc | Flour, sugar, bulk spices, granola | 5 mil | 10″ jaw |
| 10″ × 14″ | ~454g (1 lb) | ~1 gal | 300 cc | Cereal, rice, bulk legumes, powdered milk | 5 mil | 12″ jaw |
| 12″ × 16″ | ~900g (2 lb) | ~2 gal | 500 cc | Pet food, large grain quantities, oats | 5–5.5 mil | 14″ jaw |
| 14″ × 20″ | ~2.3kg (5 lb+) | ~5 gal | 2000 cc | Emergency food storage, bulk rice/wheat | 7 mil | 18″ jaw |
| 20″ × 30″+ | Industrial | 10+ gal | 2000+ cc | Agricultural products, industrial goods | 10+ mil | Industrial sealer |
Oxygen absorber values assume dry goods at <10% moisture content. Sugar, salt, and baking soda do not require oxygen absorbers — they are naturally shelf-stable and absorbers can damage leavening agents in baking products. Allow a 10–20% safety margin on absorber capacity when in doubt.
How does Mylar bag thickness affect storage life and barrier performance?
Mylar bag thickness, measured in mils (1 mil = 25.4 µm), determines puncture resistance and seal strength. Bags at 4 mil protect for 1–5 year storage. Bags at 7 mil achieve a hermetic seal for 15–25 year storage of dry goods at controlled temperatures.
| Thickness | Micron equiv. | OTR (cc/100 in²/day) | WVTR (g/m²/day) | Seal temp (°C) | Storage horizon | Best for |
|---|---|---|---|---|---|---|
| 2–3.5 mil | 51–89 µm | <1.0 | <0.5 | 160–170°C | Short-term (<1 yr) | Herbs, powders, single-serve snacks, samples |
| 4 mil | 102 µm | <0.5 | <0.3 | 165–175°C | 1–5 years | Salt, sugar, flour, dried fruit, nuts, grains |
| 5–5.5 mil | 127–140 µm | <0.1 | <0.1 | 175–190°C | 5–10 years | Rice, wheat, coffee beans, cereals, beans, granola |
| 6 mil | 152 µm | <0.05 | <0.05 | 185–200°C | 10–15 years | Dense powders, pasta, nuts, jerky, bulky items |
| 7–7.5 mil | 178–190 µm | <0.01 | <0.01 | 190–220°C | 15–25+ years | Bulk grains, long-term emergency food, whole beans |
| 10+ mil | 254+ µm | <0.005 | <0.005 | 200–230°C | Industrial / archival | Bulk rice/grains, industrial goods, cannabis |
OTR explained. The oxygen transmission rate measures how many cubic centimetres of O₂ pass through 100 in² of bag film per 24 hours at 23°C and 0% relative humidity (ASTM D3985). A material qualifies as “high barrier” when OTR falls below 1 cc/100 in²/day. Metallized Mylar at 7 mil achieves OTR values as low as 0.01 cc/100 in²/day — approximately 15,000× lower than standard HDPE film at 150–200 cc/100 in²/day. This is why Mylar extends rice shelf life to 25–30 years while a standard PE pouch lasts months.
WVTR explained. The water vapor transmission rate (ASTM F372) defines moisture ingress. At 7 mil, Mylar achieves approximately 0.01 g/m²/day — necessary for preserving hygroscopic products such as powdered milk, salt, and pharmaceutical blends where moisture drives clumping, degradation, and microbial growth.
What materials are Mylar bags made from?
Standard Mylar bags use a three-layer laminate: a 12 µm outer PET layer for structural strength, a 12 µm vacuum-metallized PET (VMPET) barrier layer with 350–450 Å of aluminum, and a 60–80 µm polyethylene inner layer for heat-sealing.
| Layer | Material | Typical thickness | Function |
|---|---|---|---|
| Outer | Oriented PET (BoPET) | 12 µm | Structural integrity, print surface, UV block |
| Barrier | VMPET or aluminum foil | 12 µm + 350–450 Å Al | O₂, moisture, and light barrier |
| Inner | Food-grade PE (BPA-free) | 60–80 µm | Heat-sealable, food-contact safe layer |
Premium bags replace VMPET with a true aluminum foil layer (9–12 µm) for superior barrier performance at the cost of opacity and reduced flexibility. Some manufacturers add an EVOH co-extrusion layer as an additional oxygen barrier for pharmaceutical and cannabis applications where OTR must remain below 0.005 cc/100 in²/day regardless of ambient humidity.
What is the correct heat-seal temperature for Mylar bags by thickness?
Mylar bag heat-seal temperature ranges from 160°C (320°F) for 3.5 mil bags to 220°C (428°F) for 7 mil bags. The PE inner layer must fully melt to form a hermetic bond. Temperature, dwell time, and jaw pressure must always be calibrated together.
| Bag thickness | Seal temp (°C) | Seal temp (°F) | Dwell time | Sealer type |
|---|---|---|---|---|
| 3.5 mil | 160–170°C | 320–338°F | 1–2 sec | Impulse sealer or flat iron |
| 4–5 mil | 170–190°C | 338–374°F | 2–3 sec | Impulse sealer |
| 5.5–6 mil | 185–205°C | 365–401°F | 3–4 sec | Impulse or direct heat sealer |
| 7–7.5 mil | 190–220°C | 374–428°F | 4–5 sec | Direct heat / constant heat sealer |
| 10+ mil | 200–230°C | 392–446°F | 5–7 sec | Industrial constant heat sealer |
Heat, dwell time, and jaw pressure are interdependent. A lower temperature held for a longer dwell produces a stronger bond than high heat at short dwell — especially for sealant layers above 40 µm. For a full step-by-step sealing guide, see how to seal Mylar bags.
What is the shelf life of food stored in Mylar bags?
Shelf life of food in sealed Mylar bags with oxygen absorbers ranges from 3–5 years for oily foods like nuts to 25–30 years for white rice, wheat, and freeze-dried vegetables — provided storage temperature stays between 4°C and 15°C (39–59°F).
| Product | Shelf life (Mylar + O₂ absorber) | Min. bag thickness | Storage condition / notes |
|---|---|---|---|
| White rice | 25–30 years | 5 mil | ≤15°C, dark, dry storage |
| Hard wheat / whole grains | 25–30 years | 5 mil | ≤15°C, dark, dry storage |
| Freeze-dried vegetables | 25–30 years | 5 mil | ≤15°C, dark, dry storage |
| Oats / rolled grains | 20–25 years | 5 mil | ≤15°C, dark, dry storage |
| Dried pasta | 8–10 years | 4 mil | ≤15°C, dark, dry storage |
| Powdered milk | 20–25 years | 5 mil | ≤15°C; WVTR control critical |
| Coffee beans (roasted) | 3–5 years | 4 mil | Use bags with a degassing valve — roasted coffee emits CO₂ for 24–72h post-roast; sealing without a valve causes bag expansion and potential seal failure |
| Nuts / seeds (oily) | 3–5 years | 4 mil | Cool temp; fats go rancid despite low O₂ — absorbers do not extend fat shelf life |
| Spices / herbs | 2–5 years | 3.5–4 mil | Room temp acceptable; potency declines over time even in sealed storage |
USDA guidance: each 10°F (5.6°C) rise in storage temperature approximately halves effective shelf life. All figures assume ≤10% moisture content at sealing time and correctly sized oxygen absorbers (300 cc per 1-gallon bag).
Can Mylar bags be frozen or used at high temperatures?
Mylar bags operate reliably from −18°C (0°F) to 100°C (212°F). BoPET film remains flexible at freezer temperatures without cracking or delaminating. The PE inner layer withstands short-term steam exposure but is not suitable for retort (pressure cooking) applications above 121°C.
Silicone-coated BoPET variants (US3394388A) extend the upper temperature limit and add grease resistance — applicable to cannabis, pharmaceutical, and industrial goods requiring autoclaving. For retort pouches, the PE inner layer is replaced with cast polypropylene (CPP), which withstands 121°C sterilization cycles. Standard food-grade Mylar bags sealed with a PE inner layer are not retort-compatible.
What Mylar bag styles and structural formats are available?
Mylar bags are available in four structural formats: flat heat-seal pouches, stand-up pouches with a gusseted base, spout pouches for liquids and fine powders, and die-cut custom shapes. Each format is available across the full range of sizes and thicknesses.
- Stand-up pouches — feature a gusseted bottom that allows the bag to stand on shelf. The gusset adds 1–2 inches of effective internal depth. Used for coffee, supplements, pet food, and snacks where retail display matters. Barrier properties are identical to flat bags of the same laminate construction.
- Spout pouches — sealed pouches with a resealable spout fitment. Designed for liquids, gels, oils, and fine powders that cannot be dispensed from a standard zipper. The spout seal requires a separate heat-seal step at the fitment ring.
- Die-cut Mylar bags — custom-shaped bags cut to a specific silhouette for brand differentiation or product-specific fitment. Same laminate options; die-cutting happens after lamination and printing.
- Child-resistant Mylar bags — incorporate a zipper mechanism that requires simultaneous squeeze-and-slide action to open. Must meet ASTM D3198 or CPSC 16 CFR 1700 for child-resistant certification. Required for cannabis packaging in most regulated markets.
Looking for custom-sized or custom-printed Mylar bags? Custom Mylar bags are available in any size, thickness, and laminate — including matte, gloss, soft-touch, foil stamp, and spot UV finishes. See also: matte vs gloss lamination, spot UV coating, foil stamping, and embossing and debossing.
How do I choose the right Mylar bag size and thickness?
Match bag size to product weight and fill volume using the size chart above. Match thickness to storage horizon: 4 mil for 1–5 years, 5 mil for 5–10 years, 7 mil for 15–25 years. Set oxygen absorber cc at 300 cc per gallon of bag volume.
| Storage goal | Recommended spec | Key reason |
|---|---|---|
| Short-term (<1 year) | 3.5–4 mil, any size | Low OTR requirement; cost-effective for high-turnover products |
| Medium-term (1–5 years) | 4–5 mil + 100–300 cc O₂ absorber | Moderate barrier sufficient; key failure risk is puncture during storage |
| Long-term (5–15 years) | 5–6 mil + correct O₂ absorber + ≤15°C storage | OTR <0.1 required; temperature control is equally important as film barrier |
| Emergency storage (15–30 years) | 7+ mil + 2000 cc O₂ absorber (5-gal bags) + cool dark storage | OTR <0.01 required; WVTR <0.01 g/m²/day; seal peel strength must meet ASTM F88 |
| Cannabis / pharmaceutical | 10+ mil or EVOH laminate + child-resistant zipper | OTR <0.005; requires ASTM D3198 / CPSC 16 CFR 1700 child-resistant certification |
Frequently asked questions about Mylar bag sizes
What size Mylar bag do I need for 1 pound of rice?
A 10″×14″ Mylar bag holds approximately 1 pound (454g) of white rice with room for a 300 cc oxygen absorber. For 5 pounds of rice, use a 14″×20″ bag with a 2000 cc oxygen absorber. Always leave 1–2 inches of headspace above the product fill line to allow for a clean heat seal.
What is the difference between 4 mil and 7 mil Mylar bags?
A 4 mil bag (102 µm) has an oxygen transmission rate below 0.5 cc/100 in²/day and is suitable for 1–5 year storage of dry goods. A 7 mil bag (178–190 µm) achieves an OTR below 0.01 cc/100 in²/day — 50× lower — making it appropriate for 15–25 year long-term emergency food storage. The 7 mil bag also has significantly higher puncture resistance for storage in rough conditions.
How many oxygen absorbers do I need per Mylar bag?
Use 100 cc per quart-sized bag, 300 cc per 1-gallon bag, 500 cc per 2-gallon bag, and 2000 cc per 5-gallon bag — for dry goods at less than 10% moisture content. Sugar, salt, and baking soda do not need oxygen absorbers. For mixed or uncertain product moisture, add a 20% safety margin to the absorber size.
What temperature do you seal Mylar bags at?
Seal temperature depends on thickness: 160–170°C (320–338°F) for 3.5 mil bags, 170–190°C (338–374°F) for 4–5 mil bags, and 190–220°C (374–428°F) for 7–7.5 mil bags. Temperature, dwell time (1–5 seconds by thickness), and jaw pressure must be calibrated together. A lower temperature held longer produces a stronger seal than high heat at short dwell.
Can Mylar bags be frozen?
Yes. Mylar bags remain flexible and intact from −18°C (0°F) to 100°C (212°F). BoPET film does not crack or delaminate at freezer temperatures. Standard food-grade Mylar bags with a polyethylene inner layer are not suitable for retort (pressure cooking) above 121°C. For freezer storage, the seal integrity is not affected by cold temperatures.
What is the shelf life of rice stored in Mylar bags?
White rice stored in a sealed 5 mil (or thicker) Mylar bag with a 300 cc oxygen absorber at 15°C or below achieves a shelf life of 25–30 years. Every 10°F (5.6°C) rise in storage temperature approximately halves the effective shelf life. Rice stored at room temperature (25°C) in Mylar bags with oxygen absorbers achieves approximately 10–12 years.
What is the difference between Mylar bags and vacuum seal bags?
Mylar bags use a multi-layer BoPET/VMPET/PE laminate with an oxygen transmission rate (OTR) below 0.01 cc/100 in²/day at 7 mil — they block oxygen through the film structure itself. Standard vacuum seal bags (PE or PA/PE) have an OTR of 1–10 cc/100 in²/day and rely on removing oxygen rather than blocking it. Mylar bags maintain the low-oxygen environment even if the vacuum is not perfect; vacuum bags do not.
Are Mylar bags food safe and BPA-free?
Yes. Food-grade Mylar bags use a BPA-free polyethylene (PE) inner layer that is the only layer in direct contact with food. The outer PET and VMPET layers are separated from the food by the PE layer. The laminate structure complies with FDA regulations for indirect food contact materials under 21 CFR 177.1630 (polyethylene terephthalate) and 21 CFR 177.1520 (polyethylene).
Can you reuse Mylar bags?
Mylar bags with zipper closures can be reused for short-term storage — the zipper reseal maintains freshness but does not restore the original hermetic heat seal. Once a Mylar bag has been heat-sealed and cut open, it cannot be re-heat-sealed to the original food-safe standard. For long-term storage applications (5+ years), always use a new bag for each fill cycle.
What Mylar bag size is used for cannabis packaging?
Cannabis packaging most commonly uses 3″×4″ bags for 1–3.5g portions, 4″×6″ bags for 7–14g (quarter-ounce), and 6″×9″ bags for 28g (1 oz). Cannabis applications require child-resistant zipper mechanisms (ASTM D3198 / CPSC 16 CFR 1700), 10+ mil thickness for maximum odor barrier (OTR <0.005 cc/100 in²/day), and opaque or foil-finish film to block light degradation of cannabinoids.
