Strictly speaking, NO system can be completely closed - for example, hot liquid in the best thermos eventually cools down - but for most purposes a system can effectively be “closed”. How would you create a system which is more or less closed with respect to:

Question

a) Heat loss?
b) Light?
c) Loss of mass?

Answer 1

a. What's wrong with a thermos for this.
b. What about a closed box?
c. Encapsulate in plastic. How about that?