Relatively speaking, the cycling helmet should be light, the lighter the better. But the light helmets will have limited chance to pass the international safety certificate test standard, then the price will be higher accordingly.
When we select a helmet, the most important is that the helmet must be passed the international safety certificate test standard, most of helmets will be around 260 g with a very appropriate price, based on this kind of weight you will not feel tired even if in long-distance riding, so do not take care of the helmet’s weight too much. Unless you are going to attend cycle race, otherwise there is not necessary to spend extra cost to buy the lightest helmets.