High humidity means that a higher proportion of air is made up of water molecules than air of low humidity. Water has a higher heat capacity than, and is a better thermal conductor than, the other things that make up air (mostly nitrogen and oxygen). So it gives and takes away thermal energy much more efficiently. Just like how, if you touch a piece of metal and a piece of plastic that are at room temperature, the metal will feel colder than the plastic, even though they are the same temperature, because the metal is a better thermal conductor and so is better able to take the thermal energy away from your hand.
thewrongequation t1_j0kt6ki wrote
Reply to How does high humidity affect perceived temperature in hot and cold environments? by MindTheReddit
High humidity means that a higher proportion of air is made up of water molecules than air of low humidity. Water has a higher heat capacity than, and is a better thermal conductor than, the other things that make up air (mostly nitrogen and oxygen). So it gives and takes away thermal energy much more efficiently. Just like how, if you touch a piece of metal and a piece of plastic that are at room temperature, the metal will feel colder than the plastic, even though they are the same temperature, because the metal is a better thermal conductor and so is better able to take the thermal energy away from your hand.