Dumbbells are perfect, no sands inside, the outside is not that plastic PVC nabîme the ground, whatever the type.
2 x 20 kg frankly for the price I find them perfect, the clamping system is super simple and fits perfectly.
The dumbbells are very large, but what counts is the result, therefore no matter the size of the dumbbell.
I advise the use of gloves when training, although aluminum bar is seized, after a certain time your hands glide with the effort.