Mylar Bags for Food Storage: Materials, Layers, and Why Construction Matters More Than Thickness
What Are Mylar Bags Made Of?
Mylar bags used for food storage are made from multi-layer laminates, typically including:
- PET (polyester) outer layers for strength and stability
- Metallized barrier layer (VMPET or aluminum foil) to block oxygen and light
- Inner sealant layer for heat sealing (BoPet preferably)
A true high-performance Mylar bag uses BoPET as part of the functional structure, not just as a label.
What Makes Mylar Bags Good for Long-Term Food Storage?
Mylar bags are effective because they reduce exposure to:
- Oxygen (causes oxidation and spoilage)
- Moisture (leads to mold and degradation)
- Light (degrades nutrients over time)
When paired with oxygen absorbers:
Oxygen levels drop to near zero and remain low due to the barrier layer.
How Many Layers Are in a Mylar Bag?
High-quality Mylar bags typically use 5 to 7 layers, including:
- Outer structural layer (PET)
- Adhesive bonding layers
- Metallized barrier layer (VMPET or aluminum foil)
- Secondary support layers (Our 7 Mil bags use Nylon for additional durability)
- Inner food-contact sealant layer (BoPet or LLDPE)
? The exact structure varies, but performance depends on:
- material choice
- layer quality
- lamination integrity
—not just thickness.
Mylar vs LLDPE: What’s the Difference?
Is LLDPE a Barrier Material?
No.
LLDPE (Linear Low-Density Polyethylene) is:
- Flexible
- Heat sealable
- Food-safe
But:
It has high oxygen and moisture permeability, making it unsuitable as a primary barrier layer.
Mylar (BoPET) vs LLDPE Performance
| Property | Mylar (BoPET / VMPET) | LLDPE |
|---|---|---|
| Tensile Strength | High | Lower |
| Puncture Resistance | High | Lower |
| OTR (Oxygen Barrier) | Very Low | High |
| MVTR (Moisture Barrier) | Very Low | High |
| Long-Term Storage | Excellent | Poor |
? LLDPE is best used as an inner sealant layer, not as the primary structure or barrier.
Does Thickness (Mil) Determine Quality?
Short Answer: No
Thickness affects durability, but not necessarily barrier performance.
A well-constructed 5 mil bag can outperform a poorly constructed 7 mil bag.
Why This Happens
Performance depends on:
- Whether BoPET is actually used
- Quality of metallization
- Layer composition
- Manufacturing consistency
? Some bags marketed as “Mylar” are actually:
- PET / foil / poly blends with minimal structural polyester
- Or primarily polyethylene-based films
Real-World Example (Common Scenario)
- A 5 mil multi-layer BoPET-based bag
→ High tensile strength
→ Low oxygen transmission
→ Strong long-term performance - A 7 mil polyethylene-heavy bag
→ Thicker but softer
→ Higher oxygen permeability
→ Lower real-world protection
? Thickness ≠ performance
What Is OTR and Why Does It Matter?
OTR (Oxygen Transmission Rate)
Measures how much oxygen passes through a material over time.
- Lower OTR = better protection
- Critical for long-term storage
MVTR (Moisture Vapor Transmission Rate)
Measures how much moisture passes through.
- Lower MVTR = better shelf stability
? True Mylar barrier systems have both an aluminum foil layer and a BoPet food contact layer:
- Very low OTR
- Very low MVTR
- High durability
How Long Does Food Last in Mylar Bags?
When using:
- High-barrier Mylar bags
- Proper oxygen absorber sizing
- Good sealing practices
Typical shelf life:
| Food Type | Shelf Life |
|---|---|
| White rice | 20–30 years |
| Beans | 10–25 years |
| Wheat | 25–30 years |
| Pasta | 10–20 years |
Are All “Mylar Bags” the Same?
No—and this is where most confusion comes from.
The term “Mylar bag” is often used generically to describe:
- Any reflective food storage bag
- Any multi-layer plastic pouch
But in practice:
Most products labeled “Mylar” do not use BoPET in their construction. This leads many to believe all Mylar bags are essentially the same.
What to Look for in a High-Quality Mylar Bag
- Multi-layer construction (5–7 layers)
- True BoPET food contact layer
- Metallized barrier (Preferably Aluminum Foil)
- Extremely Low OTR and MVTR
- Strong tensile and puncture resistance
- Reliable heat seal performance
Why Material Choice Matters More Than Thickness
If you remember one thing:
Barrier performance comes from materials and construction—not just mil thickness.
This is why:
- Some 5 mil bags outperform thicker competitors
- Not all “7 mil bags” provide the same protection
Common Questions
Are thicker Mylar bags always better?
No. Thicker bags may be more durable, but barrier performance depends on materials.
Can a 5 mil Mylar bag be stronger than a 7 mil bag?
Yes. If the 5 mil bag uses better materials (like true BoPET layers), it can have higher tensile and puncture strength.
Do Mylar bags completely block oxygen?
No material is perfect, but high-quality Mylar has extremely low oxygen transmission, making it highly effective.
Are vacuum sealer bags the same as Mylar bags?
No. Vacuum bags typically use polyethylene-based films with higher oxygen permeability.
Practical Takeaway
For long-term food storage:
- Use high-quality multi-layer Mylar bags
- Focus on material construction, not just thickness
- Pair with properly sized oxygen absorbers
Bottom Line
? The effectiveness of a Mylar bag comes from:
- BoPET structure (strength + stability)
- Barrier layer (oxygen + moisture protection)
- Proper lamination and sealing
? Not all “Mylar bags” are built the same—and performance differences can be significant.