In which of the following materials, moisture loss has to be taken care of?

Alginate impressions can distort quickly if they are allowed to gain or lose moisture, so the impression is wrapped in wet paper towels to serve as a humidor. Preoperative PVS impressions do not need to be wrapped. The preoperative impression is placed aside for later use in forming the temporary restoration. Sturdevant operative dentistry 7th Edition, Page No:120