Question: I'd like to make some extra icepacks to put in my coolbag. The 2 commercial icepacks it comes with don't maintain the temperature for long enough, so I've tried supplementing them with plastic bottles of water that I've frozen. This works reasonably well but are there other containers that would work better and is there anything I could add to the water?

Answer: 
### Use a mixture to modify the water's properties

You could use an antifreeze/water mixture that you put in a bottle. You will have a much lower freezing and higher boiling point that just water. This will allow you to keep your frozen packs at a lower temperature than plain ice for longer.

### Safety Concerns

You will also need to be **extremely careful with antifreeze around food and/or drinks as it is toxic to almost all mammals.** Other creatures may also have toxic reactions to the antifreeze. Insure that if you use a recycled water bottle that it is **extremely difficult** (*aim for impossible*) for you and/or **children** to get into it.

### Options

You could also try using alcohol instead of water. It is the same principle as mixing antifreeze with water. It is also much safer than antifreeze, but you will still need to modify the bottle to prevent child access.
The "R" value of the cooler insulation as well as the seal around the lid are important in retaining the cold. The size of the cooler is also important because the ratio of ice to the product you are trying to keep cool is also a factor. You can get pink RV anti-freeze used to winterize drinking water pipes and tanks in boats and motor homes It is I would assume non-toxic if accidentally ingested. Ice packs made from anti-freeze would probably cool faster to a lower temperature but not for a longer time.