# Ice cubes in my water bottle - large or small?

So I have a wide-mouthed 1 liter plastic water bottle that I fill each morning at work. In the freezer in the rec room, there are two types of ice cubes – the big roughly cubic ones from ice cube trays, and the small ones from the ice maker. I fill it with ice, then add water.

Big cubes should take longer to melt than little cubes But it looks like if I fill it with the big ones, there is more air space left in the bottle than if I fill it with the little ones, due to the shapes and size of the bottle.

So which should keep my water cold for longer?

Put in a few big ones, then fill with the small ones. The small ones will pack around the big ones, so you’ll get a larger amount of ice than either one separately.

At the end of the day before you go home fill the bottle about 1/4 to 1/3 with water and stick it in the freezer. Next morning you’ll have a nice solid, flat chunk of ice in the bottom.

Or drain the top tenth of the bottle and let the entire thing freeze (which is what I do)-the heat from the condensation will melt it pretty quickly, and you can supplement it with water from the faucet during the day.

I think equal quantities of big or small cubes will melt at pretty much the same rate. The rate of melting will be determined by the heat transfer from the room into the bottle.

This. Assuming your ice cubes have enough surface area to keep the entire contents of the bottle at the freezing point despite whatever heat transfer is happening at the outer surface of the bottle, adding more ice surface area won’t keep things cooler, and won’t make the ice cubes melt faster.

ZenBeam is onto something interesting, though. You can increase the length of time for which the beverage is kept at the freezing/melting point by increasing the mass of ice in the bottle - and you can do that by using a multitude of ice cube sizes, with the small ones occupying the spaces between the large ones (think of concrete, which uses aggregate in several sizes ranging from gravel down to sand). Note however that it may be difficult to achieve this without painstakingly putting in a few large cubes, then a few small cubes, then a few large ones, etc., etc.

Barring that, use ice cubes that are small with respect to the size of the bottle, since cubes that are large (with respect to the size of the bottle) won’t pack efficiently. If you are a nitpicky scientist, you can weigh the bottle after filling with large cubes, and then weigh it after filling with small cubes to see which one gives you more ice.

Since smaller cubes have more surface area they will cool the water quicker and melt quicker. Once they have melted completely the drink will start to warm. Larger ice cubes will take longer to cool the water down but also take longer to melt so that it will stay cool longer. The slightly larger amount of air should not make much difference. However it may be that you can fit more of the smaller cubes in the bottle which would make a difference.

That gave me pause for thought. Would I be right in saying that the one with more ice in, would be lighter than the one with less ice?

Or, you can measure how much water it takes to fill the bottle after stuffing it with ice. Whichever takes less water will stay cold longer. My money is on the smaller cubes.

One assumption here is that there will be enough ice to bring the water temp down to near freezing pretty much right away.

One alternate technique is to fill with ice, half fill with water, then shake, then put more ice in and top off with water. You may be able to stuff in an extra cube or two this way.

I think this is close. More ice in the bottle means the average temp is lower, but after that the rate of heat transfer will be about the same. Unless you want to drink the water while there’s still some ice in it the size of the cubes won’t matter, just the percentage of ice initially in the bottle.

Put your bottle on its side, and you’ll have a length-wise chunk of ice which will allow circulation. (I have no idea if that’s better or worse.)

Way, way, better. When I had my shop in Moab, we had a freezer that was exclusively for this. Properly managed, a gallon would last about six hours in hundred plus heat.

This. The more surface area the better transfer of heat. If taking a cooler on a picnic use water frozen it large containers. When I go camping I use gallon milk cartons.