The center strength member is an important element of fiber optical cable. For big fiber optical cable

the strength member must be upjacketed with PE. But if PE jacket is too thick

a gap will be produced and water-ingress will happen between PE and solid wire. In order to improving water-ingress

this paper has studied the cause by observing sample with microscope and introducing idea of shrinked cavity and porosity

then based on the study

the relationships between water-ingress and procress factors are discussed and explained.