Both clear and select grades of flooring sort out knots, splits and sap, but the clear grade is also checked for shading differences in the color of the wood. This extra step ensures that all of the clear-grade flooring is a uniform shade, with minimal light and dark variations in the wood. The clear grade also comes in longer lengths, meaning fewer individual pieces. This manufacturing approach further reduces variation.
There is a substantial difference in pricing between the two grades of wood, and only the homeowner can decide whether the extra price for clear grade is justified. If you are looking for the perfect, uniform, wood floor with no defects, it will definitely cost you. Keep in mind that if you are going to stain the wood, the floor will end up uniform anyway, and the price differential is probably not worth it.
By its very nature, clear-grade flooring is more rare. Wood is a natural product, and by the time you cull through it removing all the defects and variations, there is very little left. Some species such as red oak are very popular, and this further contributes to the shortage. If you choose to go with a clear-grade wood, it is not uncommon to wait a while for the product to become available.
Over time, most wood darkens and the grain structure become less prominent. Also, even though there has been a lot of progress with non-ambering floor finishes, floor coatings still dull and amber through the years. This means that the minor differences between a select- or clear-grade floor today will become even less noticeable as the entire floor ages and transforms into a more uniform color.