blockboards are mostly made from softwood (pine wood core is very popular), whereas good quality plywood is mostly made from the stronger hardwood varieties of timber. Blockboards are considered better than plywood when it making long book shelves or any other parts of furniture. Why blockboard is good for shelves is because its composition is is made up of solid rectangular blocks of wood. Lengthy plywood sheets have a tendency to sag in the middle, while blockboards are stiffer and less likely to bend.
Sizes & thicknesses:
Standard sizes available or as your require.
Furniture, partitions, racks/shelves, shutters, under layer for decorative laminates etc.