為何當飯盒從雪櫃拿出後,總是很難打開蓋子?

It is definitely about the pressure.

Accorrding to pressure law, the gas pressure is directly proportional to temp.

When you just take the box from the fridge, especially this kind of box, the gas inside the box is in lower
temp compared with room temperature, according to pressure law, the pressure
of gas inside the box is lower than that of atomospheric pressure.
(pressure law is hold as the volume of gas in the box is constant before opening the lid)

Hence the lid of the box is quite difficult to pull off.

When you rest the box in room temp for a while and let the temperature
equalized, the lid is easier to pull off.

飯盒中的蒸汽迫走了盒中的空氣， 把飯盒放在冰箱內，盒中的水蒸汽被凝聚後，氣壓自然降低了，蓋子就被吸住了。
我有方法，就是 可以用 保鮮膜蓋上而不用原蓋。 請把蓋上保鮮膜的飯盒 與 盒蓋一同放在冰箱內。 數小時後可以除去保鮮膜，然後蓋上原蓋。
:)

熱脹冷縮,so很難打開

熱漲冷縮的關係吧 ！＾＾

因為飯盒熱脹冷縮, 令盒外的壓力比盒內的大, 所以會特別難開！

yes,Is 有關盒中的壓力