The Samambu bamboo duo pen has two heads: 1 ballpoint pen and 1 inkless pen. The inkless side does not require ink cartridges or refill. The pens black graphite tip is designed to leave visible traces as it makes contact with the writing surface. Choosing a pen made of bamboo promotes making more sustainable choices, and encourages the use of renewable materials. The ballpoint pen has black ink, a nib size of 1.00 mm, and a writing length of 600 metres. Writing length inkless pen: 1500 metres.