* Polar molecules have an uneven distribution of charge, creating a positive and negative end. They are attracted to water molecules, which are also polar, and thus are hydrophilic (water-loving).

* Non-polar molecules have an even distribution of charge and lack these distinct poles. They do not interact well with water, which is why they are hydrophobic (water-fearing).

Think of it this way: oil and water don't mix because oil is non-polar and water is polar.