PAP Pens have been improved! The new formulation of Advanced A-PAP Pens is more easily removed with xylene. Additionally, water repellency and quick-drying are slightly faster than previous liquid blockers. The protocol, volume of the tube, and the diameter of the tip remain the same. Ready-to-use hydrophobic barrier pen designed for immunohistochemistry applications. This ready-to-use hydrophobic barrier pen is designed for immunohistochemistry applications. The surface tension provided by the circle, square, or any other shapes drawn to t tissue sections with the pen, ensures that only the amount of antibody solution needed for the su cient reaction will be applied. The pen is stable up to 129 °C in microwave heat. The PAP Pen is an effective tool for immunostaining procedures by the Peroxidase-Antiperoxidase (PAP) method, ABC method, LSAB method, polymeric method, immunofluorescence method, ASD method, Enzyme method and Frozen Section method. This replaces DAI-PAP-S-M.