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? How long does it take to manufacture UE Pro Custom In-Ear Monitors? Do you have a contact number? 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?