Our insulated stainless steel baby feeding bottles keep hot or cold up to ten hours. They are a healthy and eco-friendly baby thermos for mothers when going out, traveling, or for late-night bedside feeding. Our German-made anti-colic nipples are also great, shaped similar to a mother's breast. These are also very good breastfeeding bottles, holding breast milk for up to eight hours. Great baby gift for baby showers. REGARDING THERMOS FUNCTION: Please note that our bottles function like all thermoses. The greatest heat loss is within the first 2 hours, and then heat reduction slows down greatly. We recommend putting water hot enough for tea in initially (about 185F / 85C), then after 2 hours it should be around 125F / 50C. After 8 hours for our 7 oz it should then be about 110F / 45C - warm enough to still make formula. The time frame for our 4 oz bottles is 6 hours. Also filling the bottle with water will slow the temperature drop - leaving air in the bottle speeds up temperature drop. You can adjust your starting heat based on when you think you'll use the bottle - e.g. if you plan to use it in one hour, no need to put 125F / 85C water inside initially!