Disclosed are a protein conjugate with improved in vivo duration and stability and the use thereof. The items include, but are not limited to, flowers or other plant specimens. The shell may be formed from a material that would not be suitable for containing the intended contents of the container alone. The soiling check uses, only areas of the measurement window which correspond, in terms of width and position in the beam path of a light, to the areas of the checked sheet material which are checked during the checking of the sheet material. Said applied layer then expands with the applied perforated separation element to form the flat polyurethane foam.