I got this from https://www.corkway.com/articles/the-story-of-cor…
Cork has been found in tombs dating back to ancient Egypt. The Greeks and Romans also made use of it, and it has been found used in floats for fishing nets, sandals, wine bottle stoppers and personal flotation devices for fishermen. It was used to insulate homes: it made floors comfortable to walk on and was resistant to attack from insects and other pests.
Until the mid-1700’s, it was usually harvested from where it was growing naturally, but its increasing use led to it being purposefully cultivated. Cork was adopted when glass bottles needed stoppers, at a time when wine or beer was safer to drink than most water, this was vital. Starting in 1688, Pierre Perignon used corks held in place with wire to seal bottles of his latest creation, champagne.
[The strong bottles needed to withstand the fermenting process were developed in England, and the fermenting process was developed for Somerset cider production -- the Royal Society discussed these developments a couple of years before this -- sds]
Cork is the outermost layer of bark of two different species of oak tree that grow in the Mediterranean and Iberian region. It is harvested when the tree reaches 20 years, and then every 9 years after that. The productive life of the tree averages about 150 years, and the best quality cork comes from older trees, so producers are best served by allowing the trees to grow undisturbed in large stands.
Cork is harvested from oak trees using a special hatchet. Vertical and horizontal cuts are made through the bark, being careful not to hurt the living part of the tree. Usually this is done on the trunk, but on some larger trees the lower branches are also utilized. The layer is then gently removed using the wedge shaped side of the hatchet, so the trees are not damaged.
The slabs are left to cure outside for up to 6 months. This strengthens and flattens them. After that, they are treated using heat and water to remove dirt and unwanted chemicals. This leaves the cork flexible and soft.
Once it is ready, the poorer quality cork is scraped away, and the remaining portion is left to cure and dry in darkness and with controlled humidity. This high quality material will be made into wine stoppers, while the lower quality cork will be ground and made into agglomerated cork. There is no waste product.
So cork was used for lots of things.
In July 1666 Pepys bought some cork from a Mr. Hill of Thames Street. I suspect that he is the same man as John Hill, the tar merchant of Thames Street. He sounds like a general importer of industrial raw materials and Pepys probably bought all he had in stock. My guess is Coventry sent Pepys out to buy as much as he could find, rather than specifying 5 tons of it.