This is merely condensation of moisture trapped inside the blister that will clear up quickly. The presence of this fog is one sign that a good seal has been made. The paper fiber should tear in removing the blister. Test occasionally to be certain of continued good seals. Too short a sealing time.
Dwell time can vary from two seconds to four, depending on card thickness, coating, etc.
Too low a sealing pressure. We recommend 100 lbs. Too low a sealing temperature. 290 F to 340 F is the approximate temperature required to activate the adhesive and make a proper seal. A sealing fixture that is not absolutely flat, and parallel with the heated platen, may cause a spotty seal.