Mylar is not toxic. It is made from polyethylene terephthalate (PET), the same food-grade plastic used in water bottles and food containers, and it has no known toxicities when used as intended. The FDA regulates PET polymers for direct food contact, and genuine Mylar bags are approved for storing everything from dried milk to grains for years or even decades. That said, there are a few nuances worth understanding, especially around heat, sourcing, and physical hazards.
What Mylar Is Made Of
Mylar is a brand name for biaxially oriented polyethylene terephthalate (BoPET), a stretched polyester film. Its polymer backbone is built from chains of ethylene terephthalate monomers, synthesized from ethylene glycol and terephthalic acid. In food-storage bags, the structure is typically layered: an inner food-grade PET layer that touches your food, a middle aluminum foil layer that blocks oxygen and moisture, and an outer polyester layer for durability.
The inner PET layer is the one that matters for safety, and it is classified as food-grade. Genuine Mylar bags from reputable manufacturers are free of BPA, phthalates, and plasticizers, none of which are used in the production process. The concern people sometimes have about phthalates comes from the name “polyethylene phthalate,” but the phthalate in PET’s chemical structure is locked into the polymer chain and behaves completely differently from the loose phthalate plasticizers linked to hormone disruption.
The Antimony Question
About 90% of global PET production uses antimony-based catalysts, which means trace amounts of antimony can remain in the finished material, sometimes exceeding 100 mg per kilogram of PET. Antimony is a heavy metal, so this understandably raises questions.
Research on PET water bottles shows that antimony does leach, but at extremely low levels. Bottled water stored at room temperature (around 72°F) contained antimony concentrations ranging from 0.095 to 0.521 parts per billion, far below the EPA’s maximum contaminant level of 6 ppb. After three months of storage at room temperature, levels didn’t increase significantly. Heat, however, accelerates leaching. The rate of antimony release follows a pattern tied to both temperature and time, which is why storing PET containers in hot environments (like a car in summer) is worth avoiding.
For Mylar food-storage bags kept in a cool, dry place, antimony migration is not a practical concern.
Heat Changes the Safety Picture
Mylar is safe at normal storage temperatures, but the FDA sets specific limits based on how hot the material gets. For general food packaging at temperatures up to 250°F, extractable substances must stay below 0.5 mg per square inch. For oven-baking applications above 250°F, that threshold drops dramatically to 0.02 mg per square inch, reflecting the fact that heat pulls more compounds out of plastic.
This matters if you’re thinking about using Mylar in cooking. Standard Mylar bags are not designed for oven use or direct contact with very hot food. If you need packaging for high-heat applications, it must meet the stricter FDA extraction limits. For room-temperature or pantry storage, the safety margins are wide.
Not All “Mylar” Bags Are Equal
Mylar is a trademarked name owned by DuPont, but it’s used generically for any metallic-looking pouch. This creates a real problem: cheap bags sold online as “Mylar” may not actually be made from food-grade PET. They might use non-food-grade plastics, recycled materials, or coatings that haven’t been tested for food contact. A bag that looks shiny and metallic isn’t necessarily safe to store food in.
If you’re buying Mylar bags for food storage, look for ones explicitly labeled as FDA-approved for direct food contact. Reputable suppliers will specify that their bags are free of BPA and phthalates and made from genuine food-grade materials.
Long-Term Food Storage
Utah State University Extension recommends Mylar-type bags as one of the best options for long-term food storage, alongside glass jars and sealed metal cans. The foil layer in these bags dramatically reduces oxygen, carbon dioxide, and moisture transmission, which is why they’re popular for storing rice, wheat, dried milk, and other staples for years. The PET layer in contact with the food has no known toxicities.
One practical note: despite the metallic layer, rodents can chew through Mylar bags. For very long-term storage, placing sealed Mylar bags inside hard containers like food-grade buckets adds protection.
Physical Hazards for Pets
Mylar isn’t chemically toxic to dogs or cats, but it poses a serious physical danger. The FDA warns that thin Mylar-type bags, like chip bags, snack bags, and cereal liners, can suffocate pets. Dogs are especially at risk. When a dog pushes its snout into a bag to get at food residue, the thin material can seal around the nose and mouth as the animal inhales. Each breath pulls the bag tighter, like shrink wrap, and the dog can’t paw it off. This kills pets every year and can happen in minutes.
If you have dogs, cut or tear open empty Mylar bags before throwing them away, or store them in a closed trash can.