Atomic swap refill is like siphoning water from one tank to another using a clever valve system, ensuring you don’t spill a drop. In the context of Bitcoin, it involves adjusting off-chain balances (e.g., in Lightning channels or sidechains) without touching the main blockchain. Because it uses atomic swaps, both parties can trustlessly exchange assets or rebalance liquidity.

This technique can help maintain channel capacity or peg-in/peg-out between a sidechain and Bitcoin without needing a centralized exchange. It’s an elegant solution to the ever-present headache of running out of inbound or outbound capacity in a channel. While still a niche practice, atomic swap refill offers a glimpse of how second-layer technology can streamline user experience and reduce on-chain congestion.