Use as your cultures cover during fermentation. One Size Fits all - Flexible and strong elastic band tightly and securely fits many size jars (up to around 5 inches in diameter). Please measure your jars diameter before purchasing. Has a perfect worry-free snug fit. More sustainable than tossing out hundreds of coffee filters or paper towels. Unbleached and chemical-free Organic Cloth. Individually Handmade & designed specifically for the purpose of using with room temp ferments (such as milk kefir, water kefir, kombucha, sourdough, ginger beer, and yogurts like viili & caspian). Densely woven yet permeable muslin cloth, allows your culture to breathe and expire carbon dioxide but keeps outside contaminates and critters at bay. Washable and reusable! Avoid fabric softeners and heated drying to prolong life and use! :)