Woodturners - such as Robert Marichy, whose wood of choice is boxwood - tend to work with wood from deciduous trees whose resistance is generally better than that of conifers. The durability of wood i.e its resistance to alteration and degradation is a criterion to be taken into account depending on the work to be done and the destination of the finished article. The different wood species are listed by standardized durability classes. Thus light woods, or 'white woods', such as poplar or fir with a heartwood not differentiated from the sapwood have a very low durability while that of acacia or oak is naturally good.