Woodfree uncoated paper (WFU) or uncoated fine papers are manufactured using wood that has been processed into a chemical pulp that removes the lignin from the wood fibers and may also contain 5–25% fillers. Both softwood and hardwood chemical pulps are used and a minor part of mechanical pulp might be added (often of aspen or poplar). These paper grades are calendered.
Woodfree uncoated paper Wikipedia
Woodfree uncoated papers are of high quality and have a natural look and feel. The properties are good strength, high brightness and good archival characteristics. They provide a non-glare surface suitable for reading and writing.
Offset paper is a WFU paper with ISO brightness > 80% and a basis weight of 40–300 g/m2. Surface strength and low linting are the main parameters, but brightness and opacity are also important.
Lightweight offset paper, also called onionskin, has a basis weight of 25–40 g/m2 and are normally used for bibles (hence the name Bible paper) and dictionaries.