Engineers start a design by defining the problem: the criteria a solution must meet and the constraints it must stay inside, including the science that limits what is possible. The more precisely those are written, the more likely the design succeeds. A solution is then built, tested, and modified on the basis of the test results. Testing the most promising ideas and changing them step by step leads to a better design. This week you design a device that controls thermal energy with kitchen chemistry: an insulated cup that slows heat moving out, a cold pack that absorbs heat with a reaction, or a fizzing boat pushed by the gas a reaction makes. Then you write the Matter Lab report.