Well, the answer isn't that simple! Apart from personal preference, the choice depends on the environment and safety concerns, space, weight, and functionality. However, the glass and plastic are the preferred materials for the conservation jar. But glass containers are the best keeping in mind the environment as well as health. Besides, the glass will last indefinitely. So, if you discard them, they are 100 % recyclable. However, glass has a non-porous surface that doesn't absorb like plastic. Thus, it can be washed at higher temperatures with your dishwasher without melting. Besides, most of the food storage containers which are made of glass can withstand high heat without breaking.