If you want thicker eyebrows you should brush them up instead of down.
If you want thinner eyebrows then you should brush them downwards especially if you're gonna trim the eyebrows.
If you're gonna trim your eyebrows you should brush them downwards and then trim them.
However for thicker eyebrows that you're not gonna trim you should brush them upwards.
Brushing the eyebrows upwards makes them look much better as well.
I've always brushed my eyebrows upwards which gives my eyebrows a great look and much better than when I brushed my eyebrows downwards.