One frequent problem in legibility investigations is that the tested typefaces vary on too many variables. In an investigation which compares typefaces that – at the same time – vary on letter width, weight, contrast and skeleton, it will be difficult to determine precisely why the findings come out as they do, and the external validity suffers. By applying a method of integrating design practice with academic research, I have designed a new typeface family that addresses this problem of multiple typographical variables. At its current stage, the typeface family Neutral Test has seven members. One is the master typeface; three of the remaining typefaces have one stylistic feature that differs from the master (skeleton, weight, and width); and three have two stylistic features that differ from the master (weight/skeleton, weight/contrast and weight/width). In an experimental investigation where the test material is based on the different members of Neutral Test, the researcher will thus be able to identify the specific stylistic feature that causes a given difference in performance.