Soft and breathable cotton, absorbs moisture.
Aliexpress
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Here are coupons that you can use.
Updated:
Banggood
Warehouse in China.
Link: Xiaomi Baseball Cap Black
$17.99 with coupon: BGOD1
Additional Banggood coupons:
1. First page
2. Second page
Other warehouses/versions
This item is available in 2 another warehouse/versions!
1. China – Xiaomi Youpin Baseball Cap Light Gray ($-3)
2. China – Xiaomi Youpin Baseball Cap Lapis Blue ($-3)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Baseball Cap Black. The lowest price was: $7.21.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).