A non-sealed chain is a standard motorcycle drive train. It requires cleaning and lubrication regularly to maintain it's integrity. A sealed chain has drawn grease into the bushing through vacuum when it's assembled. O-rings are placed to seal the gaps around each link. This keeps the lubricant grease locked inside of the chain. It also keeps dirt and debris out of your chain. Sealed chains typically have a longer life than most standard chains, but maintenance plays a big issue in the lifespan of non-sealed chains.