According to CDC guidance, freshly expressed breast milk can be stored in a refrigerator at 40°F for up to 4 days. So 40°F is widely recognized as the benchmark for safe breast milk refrigeration. Our cooling performance tests use this threshold to evaluate whether milk remains within the recommended storage temperature range.

WONDBORN operates a dedicated Performance & Quality Lab. To better evaluate the product's cooling performance, testing is conducted using professional multi-channel temperature data loggers under controlled conditions. The results are shown in the "Lab-Tested Performance (No Lid Opening)" chart below. The results show that breast milk remains below 40°F for over 24 hours in both the top and bottom bottles under sealed conditions.

To better reflect real-world usage and ensure testing credibility, we also partnered with a third-party professional testing institution to conduct a lid-opening simulation test. The results are shown in the "Third-Party Tested (Lid Opening)" chart below. The results show that breast milk remains below 40°F for over 24 hours in the bottom bottle and 12+ hours in the top bottle. At 24 hours, even when the top bottle reaches 48°F, it remains within a safe range for short-term storage.

Overall, the WONDBORN Breast Milk Cooler demonstrates strong cooling performance and is positioned among the top tier in its category. It is designed to support a wide range of daily use scenarios, from short outings to longer trips. For breast milk transport scenarios, cooling duration can extend far beyond 24 hours, providing reliable extended cooling for long-distance.

Note: Tested by WONDBORN Lab under controlled conditions at approximately 77°F ambient temperature. Each inner bottle contains 5 oz of liquid, initially at 98°F. Cooling rings were pre-frozen at 0°F for 12 hours prior to testing.

Unlike conventional insulated containers that rely only on a vacuum-insulated body, the WONDBORN Breast Milk Cooler extends vacuum insulation to the lid as well.

By integrating vacuum layers in both the body and lid, the system forms a fully enclosed thermal barrier that reduces heat transfer from all directions, delivering 720° thermal insulation.

The WONDBORN system incorporates a phase-change cooling ring made from a water-based gel formulation, creating a stable, leak-resistant cooling medium for safe thermal performance. It delivers: more stable internal temperature control, reduced temperature fluctuations, and extended cooling duration under real-world use.

The ring is integrated around the storage chamber to provide 360° uniform cooling and works in synergy with the vacuum insulation system to slow heat ingress and stabilize the internal environment.