The simple answer: Whenever necessary! Softshell work jackets are very popular and are used in a wide variety of settings. This naturally means that softshell jackets need to be washed frequently – and that is precisely what is important for maintaining their functionality!
Warning: Never wash softshell jackets with fabric softener!!!
Fabric softener destroys the breathable properties of softshells, as a wash cycle with fabric softener leaves a wafer-thin film over the fabric of the inner membrane. This film then simply causes sweat to roll off, rather than allowing it to be wicked through the fabric to the outside during use.