Ibuprofen is relatively non-polar. This is because it has non-polar alkyl groups and a benzene ring that reduces the overall polarity of the molecule contributed by its carboxyl group. Therefore, ibuprofen is only slightly soluble in water, dissolving 21 milligrams only per liter of water at 25 degrees Celsius.
Ibuprofen's non-polar property makes it very soluble in alcohol and most organic solvents. In order to make ibuprofen more soluble and faster-acting, it can be mixed with lysine salt. Making ibuprofen into a gel and mixing it with a solvent like 2-propanol, which has greater polarity, makes it easier to absorb through the polar inner layer of the skin.