The eighteen rupa types listed below are grouped together as matter possessing inherent nature because each type has different objective qualities such as hardness, softness, temperature, etc.
The earth element serves as the support and foundation of its coexisting rupas.
The water element is the material factor that causes various rupas to come together.
The function of the fire element is to mature other rupas.
The characteristic of the air element is expansion and causing movement of other rupas.
Overall, these make up the five physical sense organs that are sensitive to sight, sound, smell, taste and touch.
Sight-sensitive rupas are found as the substance in the retina that detects light and color. Serve as physical base and gateway for visual consciousness.
Sound-sensitive rupas are found inside the ear canal and constitute the substance that registers sounds. Serve as physical base and gateway for sound consciousness.
Smell-sensitive rupas are found inside the nostrils as the substance that detects smells. Serve as physical base and gateway for olfactory consciousness.
Taste-sensitive rupas are found scattered over the tongue and serve to detect taste. Serve as physical base and gateway for taste consciousness.
Touch-sensitive rupas are everywhere on and in the organic body and serve to register tactile sensations. Serve as physical base and gateway for tactile consciousness.
Overall, sense-object rupas have the property of interacting with sense rupas. Their role is to be objects of sensory consciousness.
Tactile objects are made up of three essential elements: the earth-element, experienced as hardness or softness; the fire-element, experienced as heat or cold; and the air-element, experienced as pressure. The water-element (cohesion) is excluded because one does not sense cohesion.
The other four kinds of sense objects — visible forms, sounds, smells and tastes, are matter derived from the four essential rupas.
The two faculties femininity and masculinity, have characteristics of the female and male sex respectively. They are manifested as the cause of the feminine or masculine features of the body, and of the typical feminine or masculine behavior.
This is not the physical heart itself, but a substance in the heart that depends on the blood inside the heart. Heart rupa is assisted by the four essential rupas and maintained by life faculty rupa.
Life faculty rupa is characterized by sustaining its coexisting rupas and causing them to arise.
Makes up the nutritional substance that is contained e.g. in the edible food. Its function is to maintain the physical body.