The proteins whose R groups ionize at different pHs to obtain either a positive or negative charge are hydrophilic and due to this, they are attracted to the water molecules.
The R groups of hydrophilic proteins contain either acidic or basic amino acids.
The hydrophobic proteins are repelled by water and their R group consists of nonpolar amino acids.
When the proteins form a fist like structure, their hydrophobic R groups are hidden inside the fist whereas the hydrophilic R groups face out as it allows the hydrophilic groups to interact with the water molecules in the environment and thus, the protein obtains a stable structure.
