Highlighter contains free-flowing, water-based, fluorescent ink. Barrel has a clear window to observe ink supply. Color of the end plug & cap matches the ink color. Cap has a plastic clip. Liquid ink delivers longer write-out than reservoir-style markers. Highlighter ink will not smear, smudge or fade. Push down on the tip of the go-brite Liquid Highlighter to restart ink flow if the cap is left off for too long.