The following extract is from a publication 'From Rags to Ruin' issued by the National Preservation Office (part of the British Library):-
This is acid-free paper which, during long term storage in libraries, archives and other suitable and stable environments, has a high degree of permanence. This means that it will not discolour or become brittle with normal useage, such as examination and copying.
My History now supplies an even better grade of acid-free paper. The paper we supply is manufactured to ISO 9706 which means that it must have an alkaline reserve sometimes known as a calcium carbonate buffer thus ensuring thst it is able to withstand a certain amount external polution.