To determine whether a sealed container is made of food-grade material, a comprehensive verification is required through material labeling, certification marks, and physical testing. Below are identification methods for different materials:

Plastic sealing boxes (such as PP material)
Check the recycling symbol at the bottom
The number "5" inside the triangular recycling symbol at the bottom indicates PP material, which is the only food-grade plastic that’s microwave-safe. It’s even better if it’s labeled as "PP" or "05."
Check certification information
It should be labeled with "For Food Contact," "QS," or comply with the GB 4806.7-2016 standard. Some products will specifically state "BPA-Free."
Physical Inspection
Smell: If the packaging emits a pungent plastic odor upon opening, the material may be substandard.
Temperature Resistance: PP material can withstand temperatures from -20°C to 120°C, making it suitable for boiling water disinfection or microwave heating.
Stainless steel sealed containers (such as 304/316 stainless steel)
Look for the steel stamp.
The 304 steel stamp reads "06Cr19Ni10," while 316 is marked as "022Cr17Ni12Mo2." Grades 201 (high-manganese, low-nickel) and 430 (prone to rusting) are not food-grade.
Magnetic Testing
Food-grade austenitic stainless steel (304/316) is nearly non-magnetic and can be easily identified with the aid of a magnet.
Surface Inspection
If the surface turns black or rubs off a black powder, it may be due to leftover polishing wax—simply clean it with white vinegar plus baking soda.
Other materials (glass, aluminum alloy, etc.)
Glass: High borosilicate glass is resistant to both high temperatures and rapid cooling; the body of the kettle often features the label "High Borosilicate."
Aluminum alloy: Do not microwave, temperature-resistant from -40°C to 70°C—avoid use at high temperatures.
General Tips to Avoid Pitfalls
Request a testing report: When making a purchase, ask the seller to provide a material testing report and take a screenshot as proof.
Avoid common misconceptions:
Non-food-grade plastics (such as PVC) should not come into contact with hot food.
Plastic containers with excessive scratches or cloudiness are prone to bacterial growth and should be replaced.
Beware of false advertising: Products labeled "304" but lacking test reports may pose a risk of excessive heavy metals.

Summary: Food-grade sealed containers require triple verification—through labeling, certification, and physical characteristics—so prioritize products clearly marked with specific material codes (such as PP5 or 304/316) and certified for safety.