A leather patch hat has one weak spot, and it's the patch. The hat itself is tough. The leather is tough. The place where the two meet is a layer of adhesive, stitching, or both, and that's what gives up first when people wash a cap wrong. Here's how to clean one so it lasts.
The three things not to do
Don't machine wash it. The agitation warps a structured crown, the hot water softens the adhesive under the patch, and the spin cycle can lift a corner. Don't put it in the dishwasher. Yes, people do this. The heat and detergent are worse than the washer. Don't use the dryer, a hair dryer, or a radiator. Direct heat is the fastest way to loosen a heat-pressed patch, and it dries out the leather so it cracks.
Spot cleaning, which is 90 percent of it
Most of what ends up on a cap is sweat on the band and dirt on the bill. Mix a little mild soap (dish soap or a gentle detergent, not bleach, not anything with alcohol) into cool water. Dip a soft cloth or an old toothbrush, wring it out, and work the dirty spots on the fabric in small circles. Rinse the cloth and go over the same spots with plain water to lift the soap. Keep the patch dry through all of this. You're cleaning around it, not through it.
For the sweatband, which is the part that actually smells, flip the cap over and do the same thing directly on the band. A tiny bit of baking soda in the water helps if it's been a long summer.
The patch itself
Wipe it with a dry or barely damp cloth. That's it. Leather doesn't want to be soaked. If it gets muddy, let the mud dry completely and brush it off, then wipe. Once or twice a year you can put a pea-sized amount of leather conditioner on a cloth and rub it in lightly, which keeps the leather from drying out and actually deepens the engraving contrast. Skip anything with silicone or wax; they leave a film.
If the whole hat needs it
When spot cleaning isn't enough (the cap fell in the marsh, say), fill a sink with cool water and a small squeeze of mild soap. Dunk the hat, work the fabric gently with your hands for a minute or two, and try to keep the patch above the waterline as much as you can. Rinse in clean cool water. Don't wring it. Press it between two towels to get the bulk of the water out.
Drying
This is where people lose the shape. Stuff the crown with a clean, dry towel or a balled-up t-shirt so it holds its form, curve the bill the way you want it, and set it somewhere with airflow but out of direct sun. Overnight is usually enough. Sun fades the fabric and bakes the leather, so shade beats a windowsill.
Why ours hold up
Our caps are Richardson 112PFPs with a genuine leather patch that's sewn around the border, not just glued. Heat-press adhesive alone is fine in a dry climate. In Charleston humidity, glue is a maybe. The stitching means the patch stays put even if you ignore every word above and throw it in the washer. We'd still rather you didn't.
The same rules apply to the leather patch on our merino beanie, with one difference: the beanie fabric is a wool blend, so wash it cold on a hand-wash cycle or in the sink and dry it flat. We wrote up the details in merino vs acrylic beanies.