https://uk.finance.yahoo.com/news/ideal-grind-size-successful-aeropress-220039963.html

Whether you’re craving java at your office desk or are planning to take coffee with you to brew during your weekend camping trip, choose finely ground coffee to pour into your Aeropress. Since hot water isn’t left to seep through the beans placed inside of the contraption, look to optimize the time you do have brewing your java. Some coffee-making methods call for the use of medium to coarser grinds, but you’ll want to reach for finer particles of coffee beans to use with your Aeropress.