The density of the bubble decreases since the same number of air molecules is filling a larger volume. As you ascend to higher altitudes, the air pressure decreases. Southwest Airlines peanuts are packed at atmospheric pressure on the Earth's surface. When the packages are taken up to flight altitude they are over pressured, meaning that their internal pressure is greater than the external pressure. So they puff up.
Temperature is a measurement of the average kinetic energy of the molecules in a substance.
Heat is the transfer of energy from an object of higher temperature to an object of lower temperature. A substance that heats up quickly takes very little heat to undergo a temperature change and therefore has a low specific heat. If the desert sand heats up quickly and cools down quickly it must have a low specific heat. A conductor of heat is a material which allows heat to pass through it quickly. It takes very little heat to change its temperature and therefore has a low specific heat capacity.