The Ingress Protection rating grades the resistance and degree of protection from outside materials, such as water and dust, as classified by the International Electrotechnical Commission (IEC). The rating is split into two categories, Solid Particle Protection and Liquid Ingress Protection giving each product a two-digit IP rating e.g. IP54, IP55, IP56, IP66, IP57, IP67, IP68. It is the last digit which specifies the IP liquid ingress protection specification whereas the first number specifies the radios ability to stop the ingress of dust and fine particles. The higher the IP number the more waterproof and dust proof the radio is.
If you are looking for a robust radio you might think that you’re best to go for the highest IP available however please bear in mind that as radio handsets become more and more waterproof that their mechanical and electrical serviceability often becomes less easily undertaken and often more expensive to repair, due mostly to the design and sealing technology used in high waterproof IP rated radio handsets.