To ask how you store old letters

[crochetmonkey74]

I've got lots of lovely old letters from my much missed family members . Currently they are in a big plastic storage box but I'd like a way of storing them better.
My thought is to put them in plastic wallets into ringbinders so I can flick through and read them. I am 100% sure that I do not want them digitised or made into a book. I want to be able to hold the paper that my family held.
I think there must be some specialist things that libraries and museums use , what do I need and where do I get them from?

Don't put them in standard plastic poly pockets - it degrades and sticks to them, then takes the ink off when you peel them apart. If you want to put them in ringbinders then you can get archival polyester folders.
This is one brand: https://arrowfile.com/product/search/pocket-refill-sleeves/polyester-archival-refill-sleeves/ This company also do acid-free boxes which have ring-binder inserts.
Obviously this costs more money, but long-term is better for everything. Archives usually put them in acid-free folders in an acid free box, rather than individually into polyester sleeves, but those are slightly harder to not buy in bulk!