Unlike his opponents at Harlaw, and unlike militaries across Europe the medieval highlander was a lightly armoured fighter.
John Major one of the best sources of material on highland Scots wrote in his 1521 work that;
Tempore belli loricam ex loris ferreis per totum corpus induunt et in illa pugnant. In panno lineo multipliciter intersuto et coerato aut picato cum cervinæ pellis coopertura vulgus sylvestrium Scotorum corpus tectum habens in prælium prosilit
In time of war they cover their whole body with a shirt of mail of iron rings, and fight in that. The common people of the Highland (lit. 'wild') Scots rush into battle having their body clothed with a linen garment manifoldly sewed and painted or daubed with pitch, with a covering of deerskin."
There is quite an abundance of material both written and iconographic to help us armour our hypothetical cateran. Mail armour is mentioned not only in Major’s work but also in accounts from 1322 (Donald of the Isles) 1498 (John 10th lord of the Isles) 1564 in an accounting of a Scots pirate’s loot. Irish mercenaries in 1545 John Leslie’s description of 1578 and of course the famous Athol muster rolls includes a chain shirt. It is clear then that a shirt of maille would be quite appropriate for any wealthy cateran for the entire medieval period. and the periods before and after with decreasing regularity into the 17th century.
Maille is of course one of the medieval period’s most amazing pieces of technology. The excellent article on chain defences at my armoury is available for those who would like to know more. Maille is of a reasonable weight and is pretty much impervious to edged weapons. Broad headed arrows, spears and sword thrusts are very unlikely to pierce through the armour. Modern reenactors state that mail is of no real use without a lower layer of padded material. While I simply refute that mail is of no use without a padded layer it would be entirely appropriate for a medieval fighter to have a thin padded garment worn under the mail.
The size and shape of the mail is clear to see from this tomb image and looks very much like the mail coat worn by Durer’s Galloglass. This armour would provide excellent protection from the vast majority of weapons on the Gaelic battlefield where even great axes had thin slicing sections. Even with padding a heavy blow would incapacitate a man but the maille would protect him from the real killers of the medieval world; infection (from an open wound) and blood loss. Maille would have also allowed considerable ease of movement over the rugged terrain particularly in comparison with mainstream European harness.
Later accounts talk of plate breastplates being worn, Paul Wagner says he has images of West Highland graves wearing plate. I have not seen these; by far the most common armour of the elite appears to be a long padded garment called a cotun. This is a departure from written accounts which talk of maille. I don’t really know how to account for this many of the effigies have names and they are clearly the elite of the Isles, it may be that the islesmen wore the cotun more than maille due to the corrosive effect on metal of their sea locked homes, but then as you can see above actual Lords of the Isles are described as wearing maille. It may be that the cotun is being worn over the mail (a very protective arrangement) as the Bishop of Ross wrote "For defence, they used a coat of mail, woven of iron rings, which they wore over a leather jerkin, stout and of handsome appearance, which we call aeton. Their whole armour was light, that they might the more easily slip from their enemies' hands if they chanced to fall into such a strait."
I can find no evidence of Plate or full harness, later on evidence can be found for breastplates, made of steel, leather or even MacIain’s rawhide (actually a buff leather coat)! We should not be surprised that full plate wasn’t worn in the mountains. Full Harness was forbiddingly expensive and while not particularly encumbering was still ill suited to being worn in the mountains and would have strained the poor highland garron past endurance.
The Bascinets worn by the effigies are almost uniform in appearance an elegantly conical bascinet which would have offered good protection, visors appear not have been worn though with (perhaps) no arrow storm or cavalry charges they may not have been necessary. Alternatively they may have been left off to reveal the features of the interred. The Lanercost chronicle relates that Scots suffered from their exposed faces during the arrow storm of Halidon Hill. There is no Scottish evidence for some of the helmet designs found on later Galloglass though it would be odd if there were no interchange given the cultural closeness of Ireland and the Isles.
The wise additions of couters (elbow),and gauntlets can clearly be seen on some effigies and many wear a mail coif to protect the ,rather exposed, arteries of the neck.
It’s pretty safe to characterize the armour of the highland elite of Scotland as light but offering a good compromise between movement and protection. The nature of the country and conflicts encouraging a greater emphasis on movement.
Paul wagner has an article on how he made a cotun here
Construction methods are pretty clear from the very few which have survived (not from Scotland) being two layers of a tough linen stuffed with wool or tow. Some examples are as Major says layers of linen “manifoldly sewn”. A garment with tubes stuffed with wool would fit the iconographic evidence more and be more economical in a country with less ability to produce flax. There appears to be no difference in thickness between arm and body from the grave slabs which is odd as the garment would either be less protective than it could, be or very encumbering. Mr. Wagner solved this problem by avoiding padding areas of the arm but in a manner that does not accord with the slabs (but is probably very nice in the Australian heat). A layered garment I have has fewer layers on the arms (5) than on the body (10).This was done in historical examples and while sleeves are still heavy it is not an inconvenience. I cannot account for problem areas such as the shoulders which require great flexibility but are in considerable danger from overhead attacks. One of Durers’ galloglass also seems to have rather exposed shoulders. We should always remember that people will and did go into battle with no armor at all. In the medieval period anything you are wearing is an improvement over the clothing you WILL fight in.
Major describes the common cateran wearing similar armor so for some at least they would have had some protection. Indeed retinues of warriors are described as clad in maille so it is not a stretch to say that the warrior elite and their retinues would be armored in maille or cotton. While Irish kern were seldom depicted as armored it would seem from the sources that Scots caterans did provide themselves with some protection. Deerskin jerkins and leather coats soft yet thick would provide reasonable protection whether these were as thick and expensive as later buff coats is hard to say. The leather (if) worn by the elite may well have been, again I can’t say whether tarring leines cotun or deerskin would add to its protective abilities. I am unaware of the practice from any other culture. It would seem a wise precaution to prevent a layered or stuffed garment from becoming saturated with highland rain to prevent the weight becoming unbearable.
In my experiments with textile armours I have confirmed for myself the general view that padded armours are amazingly resistant to cuts to such an extent in fact that a padded garment could be considered more or less sword proof. They are far less resistant to arrows and thrusts. If a cateran more a maille shirt under his padded garment he would be safe from all but the most committed or heavy blows.
In conclusion, the text and the iconographic evidence do not necessarily support each other. It would appear that most members of highland martial society would be wearing similar forms of armour. Armour types were lighter than contemporary mainstream armours. Highland elite would wear maille shirts (Major) underneath longer padded garments (Leslie, tomb slabs). Lower down the social scale Caterans in general would appear to be armoured in maille for some and padded or leather armours for other. Pitch would at least have waterproofed garments and may have added some to their protective abilities. Helmets were considered essential to Irish Galloglass so were presumably worn by all who could afford one with various other plates added according to pocket.
It is unlikely that gauntlets or sabatons were worn by any other than chiefs and their immediate family.