These containers are typically made from high borosilicate glass, known for its durability and resistance to thermal shock, making them suitable for various temperatures. The lids are commonly made of transparent polypropylene (PP) with a silicone ring or trim for an airtight seal. 
Features:
They are designed to be airtight, preventing air from entering or leaving, which helps in preserving the freshness of food. They are often described as BPA-free, microwave-safe (without the lid), freezer-safe, and dishwasher-safe for convenience. 
Set Composition:
Sets often include multiple containers of varying sizes, as indicated by the "3" on the visible box in the image, suggesting a set of three glass bowls. Specific sizes can vary by brand, but common capacities include ranges like 300ml, 390ml, 690ml, and 860ml, or larger sets with capacities up to 4.6 liters.