A sweaty ball cap is a bad fit for the washing machine. The drum tumbles, the crown flattens, and the brim comes out with a new bend in it. A dishwasher does the opposite, because the cap sits still on the top rack while the spray arms do the rinsing.
That only holds for the right kind of cap, and only with the right prep. The wrong detergent, the wrong rack, or the heated dry setting will shrink the fabric or warp the bill. Here is how to wash a hat in the dishwasher safely, the two-second test that tells you whether yours qualifies, and the caps that belong in the sink instead.
Key Takeaways
- Only plastic-brim caps go in: Structured cotton or cotton/poly baseball and trucker caps with a plastic bill wash safely. Wool, leather, and vintage cardboard-brim hats do not.
- Top rack, in a cap cage: Clip the cap into a plastic hat frame on the top rack, as far from the heating element as the machine allows, so it keeps its curve.
- Bleach-free, citrus-free detergent: Pick a dishwasher detergent with no bleach and no citric acid, since both strip color out of dyed fabric.
- Heated dry off, air dry on: The drying coil shrinks cotton, warps the plastic bill, and softens panel glue, so switch it off and dry the cap over a rounded object.
Can You Actually Wash Hats in the Dishwasher?
Yes, you can wash many hats in the dishwasher, but only structured caps with a plastic brim. Everything else about the method rides on that one check, so do it before you touch a detergent cup.
Tap the bill with a fingernail. A firm, hollow click means a plastic insert and the cap is a candidate. A dull thud, or a bill that bends and feels papery, means cardboard, and cardboard is the one material this method destroys.
Caps made before 1983 often have a bill stiffened with compressed cardboard or paperboard, which soaks up water, turns to mush, and loses its shape for good, according to appliance repair guidance on this method (1). Caps built from about 1990 onward use a plastic insert instead, so a cap bought new in the last couple of decades is usually fine.
Structure matters as much as the brim. A structured cap has a stiffened front panel that holds its own shape on the rack; an unstructured “dad hat” collapses, and it does better in a mesh bag in the washing machine on a cold, delicate cycle.
The dishwasher is gentler than a washing machine because nothing tumbles. The cap sits stationary while the spray arms rinse it, so the crown and brim keep their shape.
The Risks: Does It Work for Every Hat?
No, the dishwasher does not work for every hat. Dishwasher detergent is harsh, the water runs warm, and the drying coil is hot enough to soften glue and warp plastic, so the method suits structured cotton and cotton/poly caps and very little else.
Hand wash or spot clean these instead, never the dishwasher:
- Vintage caps with cardboard or paperboard brims.
- Wool or wool-blend hats, which shrink and felt in heat and water.
- Leather hats, or caps with leather sweatbands, patches, or tags.
- Hats with delicate embroidery, sequins, or glued-on badges.
- Straw and stiffened felt hats, which lose their shape once they are soaked.
For anything valuable or delicate, the safest route is the one the hat makers recommend. New Era, the company behind on-field MLB caps, says to spot clean with cold water, a dab of mild detergent, and a soft brush rather than machine washing or fully submerging the cap (2). The same care guide rules out soaking and heat drying, and tells owners to air dry a cap on a rounded object.
Treat the dishwasher as a shortcut for everyday cotton caps, not a replacement for careful hand cleaning on the ones you actually care about. The steps below keep the risk low by controlling the two things that cause most of the damage, temperature and detergent.
What Kind of Soap Should You Use?
Use a plain dishwasher detergent with no bleach and no citric acid, and read the label before you pour. Plenty of mainstream dishwasher detergents include bleach, which is why the lemon-scented and brightening formulas are the ones to skip on a colored cap (3).
Bleach strips color on contact. Citric acid is subtler, but it is a mild bleaching agent too, so a lemon detergent fades a dyed cap a little further with every wash. A dye-free, unscented powder or gel is the safest pick, and a single cap does not need a full dose.
Can You Use Laundry Detergent?
No. Never put laundry detergent in a dishwasher. It is built to foam, and a dishwasher has no way to handle suds, so you get foam creeping across the kitchen floor and a pump working against a load it was never designed for. Stick to a bleach-free, non-lemon dishwasher detergent.
How to Wash a Hat in the Dishwasher: A Step-by-Step Guide
Four steps get the cap clean without wrecking it. Read step four before you start, because the cycle setting is where most ruined hats come from.
What You Need
- A dishwasher.
- A structured hat (baseball cap or trucker hat with a plastic brim).
- Laundry stain remover or mild dish soap.
- Dishwasher detergent (bleach-free and non-lemon).
- A “Cap Buddy” hat frame or plastic mold.
- An old soft-bristled toothbrush.
Instructions
1. Pre-Treat Stains
The spray arms rinse, but they do not scrub, so anything ground into the sweatband has to be loosened by hand first. Spray a laundry stain remover on the grimy spots, or work a little dish soap in with an old toothbrush, paying particular attention to the inside of the band where sweat concentrates. Give it 15 to 30 minutes to break down the oils before the cap goes in.
2. Secure the Hat
A plastic hat frame (often sold as a “Cap Buddy”) holds the crown’s shape and stops the cap flipping over under the water pressure. Slot the hat into the frame and clip the frame shut.
No frame? Clear the top rack and set the cap there crown down, then clip the back of the band to the prongs with clothespins so it cannot bounce around. Keep it off the bottom rack, where the heating element sits close enough to warp or melt the brim.
3. Add Detergent
Fill the detergent cup with your bleach-free, citric-acid-free detergent and close the latch. Skip the rinse aid; it is meant for glass, not fabric.
Pro Tip
4. Select the Cycle
This is the step that makes or breaks it. Pick a Light Wash or China/Crystal cycle, use cool or warm water, and switch the drying cycle off before you start it.
- Skip hot water and any sanitize option: the hottest settings shrink cotton and can warp a plastic bill.
- Turn “Heated Dry” OFF: the drying coil gets hot enough to shrink cotton, warp the plastic bill, and melt the glue holding the panels together, so the cap should come out wet and finish drying in open air (4).
How Do You Dry a Hat After the Dishwasher?
Air dry the cap on a rounded object and keep it out of the clothes dryer. Pull it from the machine as soon as the cycle stops, since leaving it in a warm, closed cabinet is how a clean hat picks up a musty smell.
Set it on a drying rack somewhere with real airflow. To hold the round shape, balance the crown over an upside-down bowl, a coffee canister, or a wadded ball of paper towels, which is the same advice New Era gives for its own caps. Expect a few hours to overnight depending on humidity, and resist the urge to speed it along with a hair dryer or a radiator; both do the damage you just avoided by turning the heated dry off.
Why Does a Hat Still Smell After Washing?
Odor that survives a wash usually means bacteria are still living in the sweatband, where salt and skin oils soak into the fabric faster than a rinse cycle can flush them out. A treatment aimed at the band fixes it; a second full cycle usually does not.
How to Fix a Stinky Hat
Two treatments work. Treat the band, then run the cycle again – it is the treatment doing the work, not the extra wash:
- Vinegar Soak: Mix equal parts distilled white vinegar and cool water. Soak the hat for 30 minutes before washing. The acid neutralizes the odor compounds instead of covering them.
- Alcohol Spray: Mix a 1:1 solution of rubbing alcohol and water in a spray bottle. Mist the inside of the band and let it dry. Alcohol kills bacteria on contact and evaporates without leaving a residue.
Removing Tough Sweat Stains
Yellow sweat stains are stubborn because the discoloration is oxidized oil and salt bound into the fibers, not loose dirt sitting on top. Before the dishwasher cycle, make a paste of baking soda and water, scrub it into the stain with a soft brush, and add a splash of vinegar. Let it bubble and sit for an hour before rinsing, then run the cycle as normal. A stubborn, long-set stain may take more than one pass, so do not judge the result too soon.
FAQs
Batter Up!
With the cap clean and the smell gone, you can put it back on without a second thought about sweat stains or odor.
Four rules keep it that way: confirm the brim is plastic, keep the cap on the top rack, use a bleach-free and lemon-free detergent, and never run the heated dry. When the hat is wool, leather, or old enough to be hiding a cardboard bill, hand washing is slower and always the safer call.
