One of the main problems with temperature sensors is the ingress of moisture which can seriously affect the sensor performance - the weakest point often being the lead/sensor interface.
ATC Semitec has developed a range of TPE encapsulated sensors where the leads and sensor are made from the same material. This creates a waterproof barrier which is rated to IP68 and can operate up to 105°C.
These sensors ensure integrity when used in outdoor locations (e.g. solar panels) as well as in under-floor heating and other HVAC applications. There are also other options such as stiff lead versions and a high temperature variant rated to 150°C. IP68 TPE encapsulated sensors are double-insulated and rated to 4kV.