When sourcing plain flip flops, the material of the sole and strap determines durability and comfort. EVA (Ethylene Vinyl Acetate) is the most common for lightweight, budget-friendly options, but for premium markets, you should prioritize High-Density Rubber or PE (Polyethylene) for better abrasion resistance. Ensure the straps are made of soft PVC or TPU to prevent skin irritation, and verify that the shore hardness of the sole is between 40-55 degrees to balance cushioning with structural integrity.