Circle pottery form/drape moulds. They are ailable in three sizes (large/medium/small) and designed so you can nest the smaller sizes within the larger size.
 
These pottery forms are made from MDF, just like any other MDF or wood products, care should be taken when drying and storing to prolong the life of these forms.
 
Specifications
Small: 20cm
Medium: 30cm
Large: 40cm
All 1.5cm thickness