What material are your custom in-ears made of? Follow Our custom shells are made of hard acrylic plastic. It’s durable, hypoallergenic and easy to clean. Related articles What is IPX technology? Do you have a contact number? How long does it take to manufacture UE Pro Custom In-Ear Monitors? Does Ultimate Ears Pro keep my ear impressions or send them back with the order? Do I need or want the passive ambient feature for my UE Pro Custom In-Ear Monitors?