Undoubtedly, most head gear was not metalic. A really well made helm would have been of all steel/iron construction, in one piece, with "nasal" as part of the whole piece. But far more common was the "spangenhelm" pattern, where a rim of metal was riveted to two cross pieces: one went over the head from ear to ear, the other went from the base of the skull to down over the nose (in earlier helms, both crossbands terminated at the rim). Helms of this type were usually worn over a leather cap, or even a cap of cloth or padded material. More expensive ones would have had curved inner plates welded/riveted into the insides of the "gaps" between the crossed bands and rim, forming a helm of no less than seven separate pieces. Like mail, this form of head protection was already very old by the Viking era (except, as far as is known, the nasal, which seems to appear no earlier than c. 9th century).

The little chess rook that is my avatar has a helm without a nasal, but there are ear and neck "flaps": the knights from the same set(s) have helms with nasals and the three ear and neck flaps; the details on them indicate that they were attached and flexible rather than welded or rivited on solidly. These chess pieces are from the Isle of Lewis and are dated to the 12th century, the outside limit of the so-called Viking era.

My favorite depiction of the famous horned Viking helms is in the movie "Prince Valiant" (1954 starring a very young Robert Wagner, co-starring an also very young Janet Leigh, Sterling Hayden and James Mason). I grin every time I see those huge, sharp horns waggling all over the place in a mob outside the castle walls. Great fun.....