Gore-Tex is a specially constructed fabric with pores small enough to repel water droplets but large enough to let body-moisture evaporate out. When sandwiched with different face fabrics ,Gore-Tex is a very comfortable ,waterproof material.
The enemies of Gore-Tex are dirt, salts and oils which, over time, will wear away the Durable Water Repellency (D.W.R.). D.W.R. promotes water beading up and running off rather than soaking into the fibres.
Frequent washings with detergent will keep the D.W.R. from breaking down as quickly. Be sure to rinse completely as detergents by nature cause water to penetrate into fabric in order to wash away dirt. Often a second wash cycle without detergent is necessary to get rid of all the detergent residue.
Everyday use and constant flexing will also cause small cracks in the D.W.R.. Drying the garment in a hot dryer will cause the D.W.R. to partially melt, re-fuse and seal over the cracks. You can also use an iron to touch up the D.W.R..
Eventually, the D.W.R. coating will wear out. There are several D.W.R. restoration products available at your local outdoor store.