Polycarbonate readily absorbs moisture from the environment. During heating, that moisture can become vapor and create internal bubbles, cloudiness, or surface rupture. The sheet may look dry and clear before it enters the oven.
Drying conditions depend on sheet thickness, coating, grade, oven capability, and supplier instructions. Temperature alone is not enough; airflow, time, loading, and moisture removal determine whether drying is effective.
Process control
Sheet should be dried according to the product data and transferred to forming with minimal re-exposure. Thick stacks, blocked airflow, or an oven that cannot remove humid air can produce a false sense of drying. Protective masking must also be approved for the drying and forming cycle.
If bubbles remain after verified drying, local overheating and incoming-sheet voids should be investigated. Increasing drying severity beyond the supplier limit can damage masking, coatings, or the sheet itself.