It has been very useful to me because it really acts as a ventilated protector for the towel from the sand. Instead of using anything else underneath, I use this and avoid the excess sand. It is quite large, but I always fold it in half and it covers two towels just fine

What others say is true, it does NOT hold the sand in any direction because it is simply a net. So, if you sit on it while wet, you will be a mess.

A plastic net it is, which unfortunately allows the sand to pass through it, so it does not serve its purpose as a 'straw'. The fact that the sand easily shakes off justifies the title 'does not hold the sand', but at the same time 'does not prevent the sand from filling your towel and swimsuit'