Varglas ES-4400 silicone rubber Sleeving is produced by curing a specially compounded silicone gum with a select catalyst on a continuous length of fiberglass braid. Most silicone rubber is characterized, chiefly, by its capability of performing satisfactorily at elevated temperatures. - Varglas ES-4400 silicone rubber, in addition to providing superior dielectric and thermal protection, at less weight, was developed to meet unusual fluid and flame resistance requirements. Its high-temperature performance places it in a 220 °C classification.