Longevity in artist paper refers to how long the paper will last, taking into account how it reacts to UV light, and whether it will fade or deteriorate over time. If you intend to exhibit your work it is advisable to be mindful of these factors and select materials that guarantee that your work will last a long time.
To ensure longevity, artist paper is typically acid and lignin-free, which helps to optimise the structure of the paper, minimising deterioration over time, including fading, yellowing, or even preventing the paper from falling apart.
100% cotton papers are often used for professional-grade artwork because they are acid-free and known to last a very long time without deterioration or discolouration. They are naturally lignin-free, and cotton’s long fibres make them far more durable than wood pulp-based papers such as wood cellulose. This is important as it allows them to erase repeatedly, lift colour with ease, scrub and scratch, without breaking down the surface of the paper.

Long cotton fibres in Jackson’s Eco Paper.
How to Choose a Paper That Will Last?
When choosing paper, you will encounter lots of different terms that are used to describe permanence:
Lignin-free
Lignin is an acid which is naturally occurring in wood pulp. If it is not removed, it will cause the paper to yellow and become brittle (newsprint is an example of a paper that goes yellow very quickly due to its lignin content).

Left: Newsprint that has been protected from the sun
Right: Newsprint that has been stored in sunlight and has turned yellow.
Wood-free
‘Woody’ components, including lignin, are removed from the wood pulp so it is only cellulose fibre.
Acid-free
This means that if the paper is ‘infused’ in water, the pH of the water is neutral (pH 7 or slightly higher). It doesn’t always mean it is lignin-free. Some papers are called acid-free because the manufacturers do not use any acids in the process, but it doesn’t guarantee that all lignin has actually been removed from the actual wood pulp. Usually, it contains a ‘buffer’, most likely calcium carbonate, which neutralises any acids present and protects the paper against acid migration.

Calcium Carbonate being added in the preparation of Two Rivers paper.
Archival
There is no universal standard of what this means in practice. But, generally, it refers to the fact that lignin and other acids have been removed and optical brighteners are not used.
Optical Brighteners (OBAs)
Brightening agents which are added to paper to make it brighter and whiter. Be aware that optical brighteners will eventually fade, causing the paper to return to its natural colour, especially if exposed to direct sunlight.