Quality Portuguese cork. Perfect to sand any surface, flat or curved, not leaving any angle marks. The cork block was especially designed to improve the grip and to develop better work on your guitar/bass. Very solid (Like a Yoga block), comfortable and soft to work with. Adapts very easily to any surface. Use it in your guitar building project too. Good for bodies, tops, necks, etc. Beveled. The set includes 4 sanding blocks. Dimensions: look at the pictures on the listings.