Abstract: Multilayer sleeves for insulating or protecting elongated substrates are disclosed. The sleeves are continuously knitted in different sections integrally joined end to end, the sections being formed of different filamentary members chosen for desired characteristics. The sleeves are formed into the multilayer configuration by reverse folding the sleeves inwardly to place one section coaxially within another. Sleeve ends may be finished with welts to prevent raveling and serve as a clinch on the elongated substrates. Rib knits are used to form insulating air pockets lengthwise along the sleeves to augment the insulating effectiveness.