Not all materials slow heat loss at the same rate. In a nested wooden box setup, a beaker of boiling water sits inside an insulated container placed in a refrigerator. The gap between the two boxes holds the insulation being tested. You check the water temperature every hour for eight hours. Batting insulation kept the water warmest across the full test. Shredded paper performed the worst. Sand did not retain heat as well as batting despite being much denser.

A thermos uses a vacuum to block heat transfer, while materials like newspaper and foam rely on trapping air to slow heat from escaping. You fill same-size jars with boiling water, wrap each in a different material, and measure the temperature every hour or two. Plotting each container's cooling curve alongside the thermos shows which material comes closest to slowing heat loss as effectively.

Different fabrics trap heat at different rates. You wrap conical flasks of hot water in five materials — cotton, flannel, polyester, wool, and Gore-Tex — and leave one flask unwrapped as the control. Each starts at 60°C. Checking the temperature every 30 minutes for two hours shows which fabric holds warmth the longest and is therefore the best at slowing heat loss.

Some materials slow heat movement into a cold object better than others. Aluminum foil wrapped around a flask of ice keeps it frozen for over two hours. Kitchen paper towels slow heat for about 90 minutes, and uncovered ice melts within an hour.

The type of glass in a window changes how well it slows heat from passing through. You build three plywood boxes fitted with single-glazed, double-glazed, and film-coated glass windows. Double-glazed glass traps an air gap between two panes. Film-coated glass adds a reflective barrier. All three boxes go into direct sunlight, and you record the inside temperature every 10 minutes. After one hour the results show which glass keeps the inside coolest.