Pentel Mechanical pencil lead High polymer lead

In 1960, Pentel was the first in the world to release "synthetic resin-based mechanical pencil refills."
Until then, mechanical pencil refills were only available with thick, easily breakable 1-1.5mm leads, and mechanical pencils were mostly "retractable" leads, where the lead was advanced by twisting the end of the pen. The arrival of the synthetic resin-blended "high polymer lead" (0.9mm) resulted in the creation of knock-type mechanical pencils that could be advanced efficiently with one hand without the need to sharpen the lead. The evolution of these refills and mechanical pencils led to the explosive popularity of mechanical pencils with the release of the "high polymer lead (0.5mm)."