Several scientific studies have established that the external ear grows throughout life. The custom moulded earplug is generally a replica: - Of a part of the auditory canal - Of a part or even the totality of the earlobe - Of the ear hook, sometimes No study has yet established that ear growth has an impact on the ear canal. As a result, Cotral Lab recommends testing custom moulded earplugs devices at the end of the guarantee period. If they are still efficient, your employees can continue using them to ensure their hearing health. However, if the test reveals that hearing protection devices do not reduce noise as much as they used to, you must renew the devices.