You must be very careful when heat pressing 100% polyester tees and uniforms. If the press is too hot or the pressure too high, you are likely to leave glossy areas on the fabric. You may also experience indented lines on the shirt where the edges of the transfer paper or heat press material meet the fabric. The best option to avoid all of this is to use kraft paper as a cover sheet and limit the time and temperature as much as possible. Heat press material such as Siser Easyweed is applied at a lower temperature than most. Also, new cold peel ink transfers can often press at much lower temperatures.