The present invention relates to a thermoforming device for thermoforming a product (1) from a plastic foil (23), and to a corresponding method. The invention relates particularly to a thermoforming process and device in which a slot (2) is arranged in a product (1) to be formed. The invention also relates to a product (1), particularly a flowerpot, manufactured using this thermoforming device or method. The thermoforming device is characterized in that the cutting sleeve (10) and cutting plate (7) and/or hold-down element (8) define an auxiliary cutting line through which the plastic foil (23) is cut in order to arrange a slot (2) in the product (1) to be formed. The functions of slot-forming and product-foil separation are hereby performed by substantially the same components.