There are various stainless steel vacuum thermoses on the market with a wide price gap. Many consumers lack knowledge of their working principles and end up spending much money on unsatisfying products. How to purchase high-quality vacuum thermoses?

First, check the exterior of the cup.

1. Check whether the inner and outer liners have uniform polishing without dents, scratches or other defects;

2. Check if the welding at the cup mouth is smooth and even, which determines the comfort of drinking;

3. Check the quality of plastic parts. Inferior plastic parts shorten service life and pose risks to drinking hygiene;

4. Check the internal tightness. Confirm whether the screw plug fits the cup body properly, twists smoothly and stays leak-proof. Fill the cup with water, invert it for four to five minutes or shake it hard to test for leakage. Next, test heat preservation performance, the core technical indicator of thermoses. Standard professional tests are unavailable during shopping, but you can fill it with hot water and touch the cup exterior. Poorly insulated cups will feel warm at the bottom after two minutes, while qualified ones remain cool.

Here are several practical identification methods:

1. Quick test for vacuum heat insulation: Pour boiling water into the thermos, tighten the lid clockwise and wait 2–3 minutes. Touch the outer surface of the cup. Obvious warmth indicates lost vacuum and poor heat retention.

2. Seal performance test: Fill the cup with water, tighten the plug and lid clockwise, then lay the cup flat on a table. No water should leak out. The lid should twist smoothly against the mouth with no gaps.

3. Plastic accessory identification: Food-grade new plastic has slight odor, glossy smooth surface without burrs, long service life and anti-aging properties. Ordinary or recycled plastic gives off strong odors, looks dull with rough burrs, and ages or cracks easily.

4. Capacity check: The depth of the inner liner is roughly consistent with the height of the outer shell (a difference of 16–18mm), and the actual capacity matches the labeled value. Some low-quality thermoses are filled with sand or cement to add weight. Note: Heavier cups do not equal better quality.

5. Stainless steel material test: Stainless steel comes in multiple grades. 18/8 stainless steel contains 18% chromium and 8% nickel, meeting national food-grade standards with anti-rust and anti-corrosion features. Ordinary stainless steel looks pale and dull; soaking it in 1% salt water for 24 hours will cause rust spots, as excessive harmful elements endanger human health.