A Viking helmet had a simple form which is a bowl with nose guard. Helmets were typically made from several pieces of iron riveted together, this style is called spangenhelm and is generally easier to construct.
The spangenhelm used a single iron band that circled the head around the brow. Two iron bands were riveted from the bottom band which crossed at the top of the helmet. These bands created four openings which were filled with riveted iron plates to create the bowl. Some helmets used hard leather to cover the four gaps to reduce cost. The nose guard was riveted to the front brow. Inside the helmet a cap made from sheepskin was used to absorb blows and sweat.
Some helmets had mail curtains or solid plates to provide significant protection against cuts to lower parts of the head and neck. Other forms of solid cheek and neck protection may have been used as well.
Source: Hurstwic: Viking Helmets
The helmet offers some good protection in battle. It gives a basic protection of one point. Helmets can be used by all characters and is fairly priced.