- Plus Office 81439 liquid ink refill for whiteboard markers - Pack of 4 orange cartridges, dry erasable and residue-free - Compatible with whiteboards, glass, melamine, and other smooth, non-porous surfaces - Easy-to-install refillable ink, extends the lifespan of your markers - Cost-effective and environmentally friendly alternative - Write and erase easily on glass, ceramic, plastic, and metal - Keeps the board clean, without stains or lines - Essential tool for offices, classrooms, and meeting rooms - Enhances visual communication and learning in professional and educational environments