Hydrophilic means "water loving". Hydrophilic polymers mix well with water. Some examples are Instant Snow Polymer, which instantly expands to 40 times its original volume when mixed with water, producing a snow-like material, and Sodium Polyacrylate, the super-absorbent polymer found in disposable baby diapers, also used in many "disappearing water" magic tricks.
Hydrophobic means "water fearing". Hydrophobic polymers will not mix with water. Magic Sand repels water and never gets wet.