Improving wool garment rain resistance
Modern wool garments have most of the lanolin extracted from the fiber during processing. You can restore the lanolin and greatly improve the water repellent properties of the garment. The method described in Camping and Woodcraft by Horace Kephart (1918) http://www.backpackinglight.com/cgi-bin/backpackinglight/reviews/display_reviews?forum_thread_id=952&cat=Books%20and%20Media&cid=62 uses highly flammable solvents, which I would not recommend.
Anhydrous lanolin isn’t as easy to find these days, but most pharmacies can order for you the Fougera brand of Lanolin, Modified, Tpoical Lubricant, which is used as a base for formulating salves and ointments. A pound canister will treat outer garments and blankets for a squad when dissolved in 5 gallons of aliphatic mineral spirits.
For a single garment or blanket buy a 2 oz. tube of a mostly lanolin-based hair dressing and thoroughly dissolve this in a quart of aliphatic mineral spirits, then gently wet and work the liquid through the fabric and gently roll and squeeze the excess solvent out WITHOUT WRINGING! Then lay the garment or blanket out on a flat surface to air dry outdoors. When almost dry to the touch hang blankets over a clothes line or place garments on hangers outdoors to air out thoroughly until all remaining solvent has evaporated.
A field expedient method I have used on single garments which also works fairly well is to emulsify 4 fluid ozs. of high lanolin content, unscented moisturizing lotion, in a pint of hot water. Apply this to the garment using a spray applicator, being sure to get good coverage of the shoulders, sleeves and back. Roll the garment up, seal in a plastic bag and place in the hot sun or heated room for 12 hours, then remove, unroll and flatten out and reshape as described above. When almost dry to the touch finishing drying on a clothes line or hanger outdoors.