Of all the materials used for clothing the human body, leather has not only the longest history but probably is one of the best-loved materials. From the era cave dwellers to the era of jet engines and chrome motorcycles, leather garments have been valued for their comfort and durability as well as their beauty and status. Thus they are expensive, long-lasting, and demand an extra degree of care.
Select a suede or nubuck treatment for a suede jacket. The split hide used to create suede would react negatively to any oil base cream, lotion, or spray and would discolour and change the texture of the leather. Only a few acryllic spray conditioners are formulated not to harm suede, so select carefully. Though they cannot be expected to make the jacket waterproof, they may improve the garment's resistance to moisture. Always test a new treatment in an inconspicuous spot--under a collar or on a hem or seam allowance.
Choose a leather protectant product manufactured without mineral oil or petroleum products for a smooth leather jacket not likely to be exposed to extreme weather conditions. These protective products, some of which are highly recommended, will not make the jacket completely waterproof but will make it water-repellent and less likely to mildew, crack, or discolour. Generally, these are sold in spray containers that recommend spraying very lightly several times, allowing the garment to dry between applications. Test-spray in an inconspicuous place first.
Purchase a conditioning and waterproofing product intended for heavy-duty leathers that may be exposed to exteme weather conditions. These organic or synthetic and organic compounds are sold in the forms of oils, waxes, or dressings and are applied with a soft cloth or brush and rubbed in as thoroughly as possible. The user then follows the application with a clean cloth or brush to remove any excess. Allow to dry overnight.
According to most authorities, no treatment will make a leather jacket completely waterproof, and the best way to protect such a garment is to keep it dry. If a thunderstorm takes you by surprise and the jacket gets drenched, hang it up and allow it to dry completely, which may take several hours. Treat it with appropriate cleaner and conditioner, and hope the additional patina makes the jacket more beautiful than before.
Leather will mildew, especially around the seams where moisture collects and takes longer to dry. Clean those places with a mixture of rubbing alcohol and water and allow to dry before using the recommended cleaner and conditioner. Never store a leather garment in a plastic bag because the lack of air circulation will encourage mildew.