When casting urethane rubber or plastic into a urethane mold, a release agent is necessary. Use Pol-Ease® 2300 Release Agent for best performance, or Pol-Ease® 2500 Release Agent if the casts will be painted. While using Pol-Ease® 2300 will result in more casts, it cannot be washed off models and should not be used if you will be painting the cast parts..