aluminum foil
Apparantely plastic keeps ice water colder because since aluminum water bottles absorbs the cold and the plastic doesnt so pretty much it keeps colder :)
aluminium foil. that's easy
A wet towel will keep drinks cooler. This happens because the sun or whatever heat source will try to dry the water from the towel. This requires heat energy, and is drawn from the towel resulting in a colder temperature in the towel itself.
Yes, because you can reuse aluminum containers for water. After a bit, chemicals in plastic will start to seep into the water.
alot
Vacuum insulated stainless steel bottles like one from Hydro Flask [see related link "hydro flask" below] or Thermos [see related link "thermos" below] will keep them coldest.
Metal - very good conductor of heat. Not a good insulator at all (Don't wrap cans in aluminum foil.) Glass - A little better resistor of heat energy transfer but still not great. Plastic - Depending on the exact material, plastic is probably your best bet. Especially if it's a foam of some sort; the air bubbles in the foam create barriers that heat energy has to cross to be able to escape.
Plastic - Foil is metallic and conducts heat easier
speaking from experience and not from science, foil is a very good conductor of heat which means it can go from hot to cold very fast (and vise versa) whereas plastic is waterproof and will keep the cold moisture (or warm moisture) in the food and we all know that water is a poor conductor of temperature thus keeping your food colder (or hotter) for longer.
The rate at which water freezes depends on the thermal conductivity of the container. Plastic is generally not very thermally conductive, whereas aluminum foil is more thermally conductive. Thus, as long as the foil is not very much thinner than the plastic, the water will freeze faster in the foil.
plastic is an insulator so it keeps you from being electrocuted.
It could be water condensation from a warmer interior forming as water droplets on the colder plastic wrap.