Basicly there are two factors from which we can say it is a good one or not:

1, Viscosity of sticker;

2, Revealing word degree.

If the two can be combined working well, then it is a good void sticker.

However, in practical use, we will meet various different materials of content where we will stick it to, such as carton(low density, high density, other special carton, etc.), plastic, glass, metal... So before we choose the void sticker, we should know what kind of material it is of the content where we will use it on, then we can find the most suitable type of void sticker. 

Above all, good technology support and accurate analysis with practical use are the main points which can help us to select a good and suitable void sticker.