 Conservation or Archival Mat Board - Constructed of 100% pure high alpha cellulose (wood pulp) and treated to be inert for up to 300 years.This is the highest quality "paper" matboard available.Acid-Free or Acid Free Lined - This material is usually lined with a wood based liner on one or both sides that has been treated to prevent "short term" acid burn - atop a recycled fiber core.