Hot Water Test: For my baseline heat test, I began by filling each thermos with boiling water and letting it sit for 10 minutes to pre-heat. You can use bleach to sanitize plastic bottle parts. As much as possible, drink from a cup and avoid drinking directly from the flask as this can cause scalding. No technical skills required! All that you need would be a little time and effort to spare. When we put the cap on the bottle, the hot air was trapped inside. (Put the balloon onto a tap and fill it until it is slightly bigger than the mouth of the jar or bottle. The bottle is made out of regular glass, so if you pour boiling water into it while the glass is cold, it can create a crack from the temperature shock. In fact, anything that can enhance your ability to venture out when everyone else thinks it’s too hot is a win. You can have boiled in shell eggs by putting a couple of eggs in their shell into the thermos, adding actively boiling water and then setting that in a towel or other insulation for about 30 minutes. Sharply knock a bottle of supercooled liquid water on the table and it instantly turns to slushy ice before your eyes. If something is cold in a thermos, it will want to stay that way. The Stanley bottle felt warm to the touch after adding hot water, thus suggesting that there is a degradation that happens over time. Don't Buy A Nalgene Water Bottle Until You Read This. Cooking with a thermos is pretty easy; in fact, if you can boil water you should be able to pull it off. The key to using this method of cooking is time, so you're going to want to plan ahead and make sure you have a good quality thermos that will retain its heat while cooking the food. - Extreme temperature retention, keeps hot for up to 7 hours and cold for up to 9 hours