Cobalt-free allochroic silica gel is the newly-developed hi-tech product whose appearance is orange or nacarat translucent glassy ball or lump granule. According to different color and performance, it can be classified into yellow silica gel indicator and allochroic yellow gel. Yellow silica gel indicator takes on orange and allochroic silica gel takes on nacarat. Owing to strong moisture adsorption and their color can change a lot along with increase of hygroscopic capacity, they are called “humidity indicator.” They not only can be used separately but also matched with fine-cored silica gel (proportion is 5% or higher).