A method for controlling density, porosity and/or gap size within a nanotube fabric layer is disclosed. In one aspect, this can be accomplished by controlling the degree of rafting in a nanotube fabric. In one aspect, the method includes adjusting the concentration of individual nanotube elements dispersed in a nanotube application solution. A high concentration of individual nanotube elements will tend to promote rafting in a nanotube fabric layer formed using such a nanotube application solution, whereas a lower concentration will tend to discourage rafting. In another aspect, the method includes adjusting the concentration of ionic particles dispersed in a nanotube application solution. A low concentration of ionic particles will tend to promote rafting in a nanotube fabric layer formed using such a nanotube application solution, whereas a higher concentration will tend to discourage rafting. In other aspects, both concentration parameters are adjusted.