A method to design hexagonal slabs with zigzag optical path was presented. Compared with COFFIN slabs, the amplitude of thermal-induced wave-front distortion is lower and easier to be compensated in hexagonal slabs. Moreover, the laser beam enters the slab at Brewster angle when it is parallel to the slab length direction, and covers the entire slab and the entrance aperture, which means the fill factor is 1 inside the slab.