There are few things as uncomfortable as walking home soaking wet in the rain. Worse still is to be wearing a long trench or rain coat that becomes soaked through with rain. Such a coat becomes less of a help and more of a burden. Many cotton raincoats are not actually waterproof, but need special treatment to be used as a raincoat. Fortunately, cotton can be easily made to be waterproof.
Clean the cotton fabric before applying the waterproofing spray. If you are going to apply the waterproofing spray to a cotton trench coat or overcoat, have it dry cleaned first.
Hang the coat outside in an open area or lay it flat on a clean table outside. Apply the spray in an even back and forth motion to fully cover the material. If the coat is laying on a table, make sure to allow the spray to dry on one side before turning it over to apply to the other side.
Reapply the waterproofing spray following the same steps as above once you find that the coat has begun to lose its ability to keep the water from seeping through.