This pack of 25 #13 Thick Dri-Tube (long quill) is a heavier-wall PVC tubing option that resists the moisture build-up that can affect hearing aid tubing over time. The thicker wall gives a firmer, snugger seal where it's matched to a sound bore drilled for thick-wall tubing, offering added durability and a more secure hold for earmolds that see heavier daily wear. Keep this size on hand for fittings that call specifically for the thick-wall variant rather than a standard-bore earmold.