Isotonic and hypertonic solutions differ in salt concentration. The concentration of salts in biological fluids, for example, in blood plasma is 0.9. A saline solution with such concentration of salt is similar to the composition of the blood plasma and it is called "physiological". If you increase the salt concentration, you get a hypertonic solution. Isotonic solution is isosmotic to blood plasma, they have the same osmotic pressure. Hypertonic solution contains the salt concentration which is more than 0.9.
For example, 2-10% is a hypertonic solution. For daily nasal hygiene procedures in children and adults, it is enough to use the isotonic sea water LinAqua Baby, LinAqua Soft or LinAqua Norm. The hypertonic sea water LinAqua Forte contains a denser concentration of salts, therefore it has a therapeutic effect and relieves congestion and swelling of the mucous membrane.