Home winemakers, brewers, and crafters - this pack of 25 size 4 cork stoppers is exactly what you need for all your bottling projects. These are real, natural corks harvested from cork oak trees in the Mediterranean, not synthetic imitations. The XXX quality means you're getting premium corks that create a tight, secure seal while still being easy to insert and remove. The dimensions are perfect for standard wine bottles: 15.8mm top diameter, 13.6mm middle, 11.9mm bottom, and 20.6mm in length. What's great about natural cork is that it's impermeable and buoyant, made from suberin which is naturally hydrophobic - meaning it keeps liquids in and air out effectively. They're safe for use with food and drinks, making them ideal for homemade wines, oils, vinegar, or any liquid you need to preserve. The natural composition allows for that slight breathing that aged wines benefit from, unlike synthetic corks. Having 25 in a pack means you can bottle multiple batches without running out, and the consistent sizing means they fit properly every time. Whether you're a serious home vintner or just need reliable stoppers for various projects, these natural corks deliver the quality and performance that synthetic alternatives just can't match. The Karter Scientific brand ensures you're getting laboratory-grade quality even for home use.