Abstract: A device measuring the fineness and/or maturity of cotton fibers contains a measuring chamber accommodating a cotton fiber sample and a tubular plunger. The measuring chamber extends between a first end closed by a wall having one or more vent holes and a second end opposed to the first end and hermetically closed. The plunger penetrates within the measuring chamber through the second end to run at least two strokes of predetermined lengths and has an inner channel extending between a tail portion and a perforated head portion placing the inner channel in fluid communication with the measuring chamber. The device further contains a reservoir placed upstream of the inner channel and in fluid communication with the inner channel; a pump filling the reservoir with air from an environment; and a flow regulator placed downstream of the reservoir and upstream of the inner channel.