Regarding word usage in Grimnismal, the Old Norse word translated as "corslets" is "brynjum" which is best translated as "mail shirts". The base word, "brynja", although later used as a more generic term for "armour", was in these earlier periods solely used for mail armour.

Looking at the question of what alternatives to mail there were, the short of it is that we simply don't know. Not only don't we have any archaeological evidence of non-metallic armour from the period, but we don't have any literary descriptions or artistic depictions of it. The archaeological evidence is not in itself a smoking gun saying that the Vikings didn't wear some kind of textile or leather armour, because even in periods where we know textile armour was worn (the mid-12th to the 15th centuries, for example) we lack almost all physical evidence. Aside from a sleeve from an aketon (which was padding rather than a protective garment) dating from the 12th to the mid 13th century and the leather facing of some kind of quilted garment dating from the mid to late 12th century - whether padding or actually protective we don't know - no stand alone textile armour exists before the 15th century.

The lack of references in text and art are, similarly, not proof of a lack of textile or leather armour usage. The earliest literary reference to textile armour in the Middle Ages dates from the early 1130s, but we don't see any artistic depictions until ~1200 and these don't become common until well into the 13th century. Scandinavian artwork of the period that has survived to the present, mostly rock carvings and the occasional tapestry fragment, isn't particularly well suited for capturing fine details (like textile or leather armour) and so we can't draw any conclusions from this. By the same token, the first written works which describe armour date from well after the Viking period and, as such, are useless to us in this.

As a result, a number of authors over the years have assumed that the vikings wore some form of textile armour, more or less on the basis that it makes sense that poorer vikings would want some kind of armour to go into battle (two recent examples are Kim Hjardar and Vegard Vike's Vikings at War and Gareth Williams' Weapons of the Viking Warrior). I tend to disagree with this view, as there's plenty of evidence of men fighting throughout history without armour, including close up work with spear or sword. Additionally, the shield that every viking use in war served as an excellent piece of armour, keeping the enemy weapons at a distance and stopping spears and arrows far more effectively than even mail could.

The sole exception to our ignorance of other forms of armour is lamellar armour. We know that some was worn by the Birka garrison in the 10th century, although these could quite easily have been Khazar or Magyar mercenaries hired as part of the garrison. However, Gerald of Wales speaks of some Danes who wore "iron plates knitted together" during an attack on Dublin in 1171, and not only was a complete set of lamellar armour found at Visby, but sufficient lamellae were distributed in Common Grave 2 to suggest that this was not a unique example. However, none of this should be taken to indicate that lamellar armour was common. Gerald of Wales might be simply referring to a very early coat of plates, while the gap between the Birka and Visby finds is in the region of 400 years. So, while I have little doubt that lamellar armour was worn, I also don't think that it was particular common, especially in the early Viking period. I'd go so far as to say that it's highly unlikely to have been worn prior to the 10th century, and maybe not even then.

Suggested Reading

• Vikings at War, by Kim Hjardar and Vegard Vike
• Weapons of the Viking Warrior, by Gareth Williams
• Medieval Military Technology (Second Edition), by Kelly DeVries and Robert Douglas Smith
• Steppe nomadic armour from Birka, by Niklas Stjerna, tr. Magnus Ritzen
• Viking Weapons & Warfare, by J. Kim Siddorn (2003 edition)