As is it with many components of a bamboo fly rod (the agate in nickel silver stripping guides, patterns in wood inserts, the bamboo itself, etc.), cork used in cork grips is a natural product so the quality varies from ring to ring and from grip to grip. Presently there are no industry standards for grading cork grips or their component cork rings, so the more you can know about what you are buying the better off you are. Perhaps the most you can hope for is a solid return policy and a supplier you can trust.
Many believe the best quality cork for cork reel seats comes from Portugal. Portuguese cork may or may not be the best, but Portuguese Cork accounts for about 50% of the world’s annual cork production (a little over 300,000 tons).
Cork comes from the cork oak tree (Quercus suber). After about 25 years, the cork bark can be harvested for the first time. Since bark removal (if properly done) doesn’t harm the tree, the process can be repeated every 9-12 years over the productive life of the tree. The harvested cork is used in many products other than fly rod cork grips, perhaps the best known being corks for wine bottles.
Lacking accepted industry standards for grading cork rings and cork grips, suppliers and/or retailers apply such terms as Flor (usually reserved for the top quality), Superior, AAA, or some such rating which turns out to be quite subjective. If the dealer is reputable, then buying Flor grade cork (for example) will get you the best cork from that dealer at that particular time. But it may not be the same quality (better or worse) than Flor cork from another reputable dealer. And due to natural fluctuations in the quality of the cork rings or cork grips provided by importers or manufacturers, Flor cork purchased from the same dealer at a different time can be just as different as if you were buying from a completely different dealer. So until industry standards are established, buying from a good source who will allow returns if you aren’t satisfied may be your best bet.