The resistance of insulators is substantially affected by both temperature and humidity. Humidity can significantly lower the effective resistance of insulators and cause an increase in leakage current around the affected material. When water molecules settle on the surface of a given material, such as the plastic packaging and PCB, a parallel and more electrically conductive path is created. Effective guarding techniques and appropriate materials can help mitigate this behavior in the sensitive applications.

In some cases, water molecules can also penetrate the surface of a given material. The water molecules in the material increase the conductivity of the body of the material and a reduction of resitance is established across all adjacent nodes. Contrary to surface level leakge paths, leakage through the material cannot me mitigated with guarding techniques. Use PCB materials with low humidity absorption properties to reduce moisture related errors.