Abstract: There is disclosed a writing unit better known as a refill for writing instruments, comprising a cap housing a cartridge composed of an ink accumulating capillary body, and a smaller diameter, greater capillary capacity ink feed member connected between the writing tip and the adjacent end of the capillary body. Air enters the case through a hole axially between the writing tip and the adjacent end of the capillary body and the forward end of a tubular cap sealingly engages the case, the tubular cap covers the portion of the feed member otherwise in contact with the atmosphere and the adjacent end of the capillary body so as to reduce evaporation of ink from capillary parts.