A note on $\chi$-unbounded classes of geometric graphs

We show that there exist infinitely many classes of intersection graphs of geometric objects that are not $\chi$-bounded – namely, $d$-CBU graphs for $d\ge 3$ – and each is incomparable with the class of Burling graphs. This answers a folklore open problem on whether Burling graphs are the sole source of unbounded chromatic number among geometric intersection classes.