Millboard in various sizes and thicknesses
Millboard is a better quality board than greyboard. Roughly speaking it is greyboard that is more compressed during manufacture, and (sometimes) slightly more smoothly finished maybe only on one side). There may be slightly more "glue" in the mix, before making. It is likely to be made with a high percentage of recycled materials, and coloured flecks of previous papers can be made out. These can be seen in our photograph. It is made in various thicknesses, but they should normally be treated as nominal, or guidance values.
Millboard quality will vary between batches and makers. Our present materials have one side quite smooth. This can be seen in the picture, where the central board catches the light more than the others. The slight roughness of the other boards can also, possibly be seen. Consideration between newspaper and glossy printing paper is a fair way to describe the differences.
In use millboard is invariably covered with a more appropriate medium, as in the board covers of books, where its extra stiffness and density makes it less likely to bend.