Rectangle 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: 20x10cm
Medium: 30x15cm
Large: 40x20cm
All 1.5cm thickness