The temperature is set too high on the heat press. Make sure you test the temperature using heat test strips or a heat gun. If the temperature is too hot, it could scorch the shirts and the ink. There is too much pressure being applied to the shirt during fixing. When heat pressing your shirts, make sure you do not apply too much pressure. You should not have to put a lot of pressure to clamp the heat press down. Wrong type of paper used to protect the shirt when using a Heat Press for final fixation. Make sure the paper that is used for fixing is either a Teflon pad or Silicone treated paper. We recommend our protective sheets.