For any given substance, the heat capacity of a body is directly proportional to the amount of substance it contains (measured in terms of mass or moles or volume). Doubling the amount of substance in a body doubles its heat capacity, etc.
Conventional soft contacts can last up to a year; conventional rigid gas permeable (RGP) contact lenses can last even longer. Frequent or planned replacement contact lenses last one to several months. Disposable contacts last from one day (daily wear) to up to two weeks (extended wear).
Over time, the seal on these containers becomes weak, which can lead to contamination of the saline solution and lens. The expiration date indicates the last month and year you can consider the lenses free from contamination. Hard, or gas-permeable, contact lenses usually do not have an expiration date. Manufacturers make these lenses to order and ship them dry. Hard contact lenses are not stored in saline solution, which eliminates the risk of contamination before usage. The consumer is responsible for sterilization.