Abstract: An inexpensive writing pen for low viscosity liquid inks and formed with an internal ink reservoir and a capillary system for admitting air into the reservoir. The ink reservoir is formed directly by the walls of the pen body, which form an internal cavity. Transfer of heat from the writer's hand into the region of the ink reservoir is inhibited by providing projection elements and intervening air spaces, which form the effective outer surface of the pen body. Preferably, the material of the pen body extends substantially above the upper limits of the internal ink reservoir, and is provided in those upper areas with similar projections and spaces, facilitating transfer of heat from the pen body into the ambient. The arrangement minimizes variations in the pen characteristics resulting from transfer of heat from the user's hand, which can become relatively more acute as the volume of air within the ink reservoir increases as a result of ink consumption.