I use the word heavyweight in the sub-head since this type of mitsumata paper is about the heaviest made. Although its grammage is around 130gsm it compares in feel and strength to a 'normal' 250gsm ~ or thicker ~ board. As with all fibres made from the Asian trees ~ shrubs ~ and grasses ~ the paper is remarkably light and durable. European wood-pulp is heavier than most of the the fibres used in Asia.
In the UK government archives are preserved on the strongest material available ~ dried animal skins. In Nepal they have used their natural papers such this ~ known there as Argeli ~ or Lokta  for centuries. I have heard that the Nepalese mistsumata fibres are exported to Japan ~ the home of hundreds of different home-made papers ~ for use in their banknotes.
The smooth surface of this board is obtained by rolling the almost dry sheets onto smooth steel plates and leaving them to air-dry in the sun. One surface is slightly smoother than the other
We also have stocks of a sister type of paper ~ also made in the same family run mill close by Katmandu  . 720 x 560 mm, 28 x 22 inches (approximately)