The history of Viking Helmets is very fascinating and quite a mystery. First, they did not wear horned helmets. These seem to be a modern invention for Wagner's Der Ring des Nibelungen.
What helmets did the Vikings wear? Well there has only been one complete Viking Age helmet found, the Gjermundbu helmet. We stock several replicas of this helmet. Given how many other finds there are with lots of weapons and other items this is very strange. There are some amazing pre-Viking finds of helmets in Scandinavia from Vendel. These are all incredible helms which are richly decorated. Several of these have decorations very similar to the famous Sutton Hoo helm found in Suffolk, England. So, before the Viking Age they certainly did bury their dead with helmets.
There are lots of theories on why more helms have not been found. Perhaps during the Viking Age it wasn’t a custom to bury the dead with a helm. Maybe they were handed down from generation to generation and modified with the times. It is possible most of them were not iron and made from something like leather that would have decomposed without a trace. Leather helms wouldn’t be as strong as iron, but they would be lighter and could still help with glancing blows and blunt trauma. Or perhaps the Vikings rarely wore helms. At this point we cannot say for certain.
It is common to assume they would have worn helmets like those used in other parts of Europe at the time. Our spangenhelms would be a good example of a commonly used helmet during the time. More specifically the 11th century Moravian nasal helmet or the helmet of St Wenceslaus from the 10th century.
The Bayeux tapestry and other artwork from around the time depict many warriors wearing helmets. The sagas also often mention helmets being used.
Perhaps one day we will have an answer for this mystery.