Double lip used in application where additional protection against contamination is required, Dual lip rotating in same direction for good sealing performance, high operational reliability, it is mainly used to retain oil/grease inside a machine while providing additional protection against dust, dirt, moisture, and other contaminants entering from outside. A double-lip seal is suitable for applications where you need both fluid retention and protection against external contamination. PTFE double-lip designs can be particularly useful where low friction is required. double-lip seal keeps the lubricant in and provides an additional barrier against contaminants coming in.