Why Compostable Bags Crack in Freezers — and How Material Science Solves It

At Torise Biomaterials, our R&D team views this "shattering" effect not as a failure of eco-friendly technology, but as a hurdle easily overcome with the right material knowledge and application. By understanding the science behind the cold, we can ensure that sustainability and functionality go hand-in-hand.

To solve the problem of brittle bags, we must look at the Glass Transition Temperature (TG). This is the temperature at which a polymer shifts from being flexible and "rubbery" to being hard and "glassy."

Most compostable films are blends of PLA (Polylactic Acid) and PBAT (Polybutylene adipate terephthalate).

• The Challenge: Pure PLA has a high of approximately 55°C (131°F). In a refrigerator or freezer, PLA is far below its transition point, making it naturally prone to snapping.

• The Solution: PBAT features a as low as -30°C. Our R&D team optimizes our cold-storage formulations by increasing the ratio of high-quality PBAT to ensure the material remains elastic in sub-zero conditions.

Professional Guidance: If you have specific deep-freeze requirements, look for products labeled as "High-Toughness" or "Freezer-Grade." [Discover Our Compostable Produce Bags.] Torise Biomaterials offers customized formulations where we adjust the PBAT and bio-based polyester ratios to meet your specific temperature thresholds. Contact our technical consultants for a custom blend.

The structural integrity of a compostable bag is influenced as much by how it is handled as by how it is made. Our engineering team suggests the following protocols to maximize performance.

• The "Tempering" Minute: The most critical moment for a bio-polymer is the first 60 seconds after it leaves the freezer. We recommend letting the bag sit at room temperature for 1 to 2 minutes. This allows the molecular chains to regain their flexibility before the bag is unfolded or opened.

• Managing Sharp Edges: For frozen proteins with bones or sharp edges, a standard film may struggle. Engineer’s Tip: Use our PLA-coated paper bags as a primary wrap. The paper provides superior puncture resistance, while the PLA coating maintains a moisture barrier, allowing you to place the item securely into a secondary compostable bag.

• Condensation Stability: While "sweating" occurs during temperature changes, our materials are engineered to maintain structural stability. However, patting the bag dry after removal prevents accidental slips and tears.

• Leveraging Breathability: Compostable bags are naturally more gas-permeable than PE plastic. This is an advantage for leafy greens and mushrooms, as it prevents the buildup of ethylene gas.

• Pre-Storage Prep: For maximum shelf life, ensure produce is dry before bagging. Excess surface water can lead to localized softening of the material over long periods.

One of the most frequent questions we receive is whether a bag will begin to rot while inside the refrigerator.

Our R&D team holds that under the dry, cold conditions of a household refrigerator, Torise compostable bags maintain their physical properties and stability for weeks or even months. The industrial composting process requires a "trinity" of high microbial activity, high humidity, and sustained heat (above 50°C)—conditions that are the polar opposite of your kitchen's cold storage. You can trust that your packaging will remain a reliable barrier until it reaches its end-of-life in a composting facility.

Honesty is the foundation of the trust we build with our partners. While we are pushing the boundaries of biopolymer strength, compostable films currently have different performance profiles than traditional, non-degradable PE plastics. They are optimized for the circular economy, meaning they are designed to protect food during its usable life and then return to the earth. For ultra-long-term frozen storage (exceeding one year), we recommend contacting us for a detailed discussion to ensure the barrier properties meet your needs.

Choosing the right compostable packaging is an art that balances material science with daily habits. Whether you are a retailer looking to reduce your carbon footprint or a consumer seeking a plastic-free kitchen, the key is selecting the right material for the right environment.

Not sure which solution fits your specific cold-chain needs? Whether you are bulk-freezing inventory or optimizing fresh produce packaging for retail, our technical advisors are ready to assist. We provide free consultations to help you find the perfect thickness and blend for your application.