Medical grade. Hypoallergic Material. NOT only about sound, but user experience as well. Tang SanCai uses medical grade silicon to minimized the chance of any kinds of allergy.. Precise Bore Diameter. The Diamater of the bore plays a huge part of sound balancing and preformance. During development, we have analyzed over 10 types of eartips on the market and we think the measurments are right on spot for the balanced version of Tang SanCai.