What makes a wool coat Waterproof?

  Everyone wants to stay dry. Which is why buying a coat that actually keeps the rain out is essential when living in any wet climate. No one likes to wear a coat thinking its waterproof only to realize 5 minutes into a downpour that you're soaked! This begs the question, what makes a coat waterproof? Here we will explore the foundation for how waterproof fabric is make, to allow you to make sure your next coat you purchase will actually keep you dry. (After the article I will provide you with some options in the market that we recommend you take a look at.)

🌱 Baseline: How Wool Handles Water

• Natural Oils (Lanolin): Even before wool is spun and woven, the fibers have an inherent waterproof hydrophobic quality. This is because the sheep produce a substance called lanolin on their coats which keeps the animal from getting wet, allowing it to stay dry and warm in cool rainy and climates. However, during the weaving process the wool is washed and most if not all the lanolin is washed away to use in mainly cosmetics.

• Absorption Capacity: Wool can hold up to 1/3 of its weight in water before it feels wet. That means it stays warm and insulates even when damp, which is why traditional winter wool coats work fine in snowy conditions.

• The Limitation: In heavy or prolonged rain, untreated wool will eventually soak through. That’s why a standard wool coat can't be “waterproof.”

So, if you want a coat that truly keeps rain out, you’ll need one that’s either treated with special finishes or built with additional waterproofing layers.

🧥 What Makes a Coat Waterproof?

There are two things that a coat has to do to be truly waterproof:

1. The fabric has to stop the water from getting through, and

2. Have seams, zippers, or stitching that will keep the water from leaking through.

There are two main ways this is done:

1. Waterproof Materials (Built-in protection)

Some fabrics are naturally waterproof, especially when they’re specially engineered.

Examples:

• Rubberized fabrics (like old-fashioned raincoats)

• Membranes like Gore-Tex or polyurethane films, where a special layer is added under the outer fabric

• Specialized high-density wool fabrics  (e.g., gabardine) where the fabric is woven especially tightly to avoid any water from seeping through

There are very tiny pores in these fibers (or none at all) that block water droplets but can still let body moisture (like sweat vapor) escape. This means the rain is kept out, and it avoids the stuffy buildup inside your coat. These materials keep you dry because they are engineered to keep out the water from their very inception. Any coat you buy with these qualities is sure to do their job.

2. Water-Resistant Fabrics (Treated for Protection)

The next type of coat you can have are coats where the coat fibers are wool or cotton, fibers that are not naturally waterproof, but are treated with a special coating to keep the water out.

This coating is usually called DWR — Durable Water Repellent.

• DWR forces the water to bead up and roll off instead of soaking in.

• Your coat won't stay waterproof forever, and will eventually need to have the DWR reapplied to maintain its hydrophobic properties. 

• Your coat can resist light rain or short exposure, but not a long downpour.

🔍 How to Tell if a Coat Is Truly Waterproof

When you’re shopping, here’s what to look for:

⚠️ Watch out: If a coat only says “water-resistant”, it will handle drizzle but not a downpour.