Lack of maintenance is the leading cause of dryer fires, and lint is the leading material to ignite.  Dryer fires can be caused by insufficient airflow and lint build-up in the dryer or in the exhaust duct.  Reduced airflow and lint build-up cause overheating of the exhaust environment demanding excessive cycling of the high temperature thermal cut-off switch leading to failure.  Overheated clothes dryers can cause fires.  Fires can spread to the wall or other combustible materials through the plastic hose melting and the lint inside igniting.  The use of proper venting materials is the first step to ensure safe and efficient dryer operation.  Avoid flexible plastic venting material which is combustible.  To achieve optimal air-flow and reduce lint build-up use the shortest distance with all-metal dryer venting material.