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).
The introduction of  extended wear  enabled wearers to sleep in their contacts. Now, two types of lenses are classified by wearing time: 1  Daily wear  must be removed nightly. 2  Extended wear  can be worn overnight, usually for seven days consecutively without removal.