Disclosed herein are flame-retardant electric cables (10) having a core containing an electric conductor (11) and an electrically insulating layer (12) made from a flame-retardant polyolefin-based composition including a) a cross-linked polyolefin as base polymer, b) silica, and c) carbon nanotubes, wherein the amount of silica is from 5 wt % to 10 wt % of the polyolefin-based composition, and the amount of carbon nanotubes is from 0.5 wt % to 2 wt % of the polyolefin-based composition. Such cables have improved flame retardant performances, especially regarding a lower occurrence of droplets during burning, which render them capable of being certified in higher classes of the current international standards, for example of the standard EN 50399:2011/A1 (2016).