The default value depends on the data type's byte width: # Python arr16 = va.array(np.arange(4, dtype=np.int16), dtype=va.int16, axis=va.axis()) print(arr16.tkeep) # [3 3 3 3] (2 bytes -> 0x3) % MATLAB arr16 = varray.int16([1 2 3 4], axis=varray.axis()); arr16.tkeep % [3 3 3 3] (2 bytes -> 0x3) arr32 = varray.int32([1 2 3 4], axis=varray.axis()); arr32.tkeep % [15 15 15 15] (4 bytes -> 0xF)