The entry level natural cork. This is the lowest grade natural cork we recommend. Corks are typically graded on a scale of 1-10, 1 being the best, based on the degree of porousness that the actual punch of cork exhibits.The Grade 4 corks show average porousness and is a little below the quality of cork used in many commercial facilities. They will normally seal perfectly, however if you are looking for a cork for extended aging of 5-7+ years, consider a grade 3.