Summer-Ray 3mm Assorted Color Flat back Pearl In Storage Box (Color Collection #2) 29% OFF for a limited period and until stocks last. Normally priced at $15.49. 5000pcs of 3mm acrylic flat back pearl. These flat back pearls are made of plastic. 10 different colors. Come in a plastic storage box. The plastic storage box measures approximately 5 inches by 2.75 inches by 1 inch in size. Approximately 500pcs flat back pearl for each color.