A tube assembly (1) comprises a dummy tube (2) formed from extruded medium density polyethylene and five primary tubes (3), also formed from extruded medium density polyethylene, and placed around the dummy tube (2). The primary tubes (3) are also provided with a co-extruded lining (not shown) on the internal surface thereof to minimise static attraction and friction between the tubes (3) and optical fibre units (not shown) subsequently installed into the tubes (3). The tubes (2, 3) and a rip cord (4), for subsequently removing the covering layers of the assembly to gain access to the tubes (2, 3), are surrounded by an outer sheath (5) formed from extruded medium density polyethylene. The outer sheath (5) is provided with a non-metallic water barrier (6), and is surrounded by a lubricant polymer layer (7) containing a polyethylene based lubricant compound, the active constituent of the lubricant being an organic silicone slip agent.