Optibor reduces the linear coefficient of expansion in glass when silica is replaced proportionately with boric acid, facilitating a thermal fit in ceramic glazes and heat resistance in borosilicate glass.

When heated above 212°F (100°C) in the open, Optibor gradually loses water, first changing to metaboric acid (HBO₂), of which three monotropic forms exist. These metaboric acid forms can volatilize at >600°C during heating, leading to potential losses of boron emissions. Dehydration stops at the composition HBO₂ unless the heating time is extended or the temperature raised above 302°F (150°C). On continued heating and at higher temperatures, all water is removed, leaving the anhydrous oxide B₂O₃—an amorphous glass that begins to flow at 842°F (450°C). The amorphous form of Optibor TG has no definite melting point, softening at about 617°F (325°C) and becoming fully fluid at about 932°F (500°C).

Aqueous solutions of Optibor are mildly acidic, the pH decreasing with increasing concentration. Optibor’s sieve specification is U.S. sieve No. 20, with a mesh size of 0.850 mm and a retained guarantee of ≤ 2.0%. Optibor forms boric oxide above ~300°C, which softens and begins to flow between 350°C and 500°C.

Optibor is ideally suited to bulk transfer. Optibor shows little tendency to cake, except after prolonged storage or severe wetting.