The process of killing pupa without changing the cocoon shell layer is known as

The process of killing pupa without changing the cocoon shell layer is known as Stifling.
Stifling treatments are applied to silk cocoons to kill the pupae, preventing the emergence of moths and allowing them to preserve the silk during long periods.
All of them involve the application of aggressive steps, such as sun exposure, hot steam from boiling water or hot air, during hours or even days.