Shields seem to have been used universally by all warriors. From the first to the tenth century round shields seem to have been the norm, being either flat or 'watchglass' shaped in cross-section. They are always shown with a boss and all the examples found have been of planked construction although there is some evidence to suggest a plyed construction would make the 'watchglass' shape easier to make. Some shields were edged with a rim of sewn thick leather or hide to strengthen them whilst others were possibly faced with leather or rawhide. The Romans had leather shield bags / covers to protect them from the elements, and were fairly elaborate with specially sewn parts in the shape of the boss, and their unit symbols on them. Perhaps a version of these was what the chroniclers meant when they refer to leather covered shields.
Traditionally shields are described as being made of linden (Lime) wood although most of the shield boards found have been made of spruce. It is likely that other timbers may also have been used such as Alder and Poplar. These timbers are not very dense and are light in the hand. They also have a characteristic in that they are not inclined to split unlike Oak. Also, the fibres of the timber bind around blades preventing the blade from cutting any deeper unless a lot more pressure is applied. Round shields were typically 80 - 90cm (31" - 36") in diameter and constructed from 6 - 10mm (1/4" - 3/8") thick planks.
Most shields are shown in illuminations as being painted a single colour although some have a design painted onto them; the commonest designs are simple crosses or derivations of sun wheels or segments. The few round shields that survived have much more complicated designs painted on them and sometimes very ornate silver and gold work applied around the boss and the strap anchors. It is likely that most shields had an attached leather strap to enable it to be hung over the shoulder. This strap comes in useful for carrying the shield whilst walking or for when you are riding a horse as it leaves your hand free for the horse's reigns.
Practical tests have shown that lime wood shields are naturally very good at absorbing blows and resist splitting, and they are particularly good at trapping spears when you parry with them (the Saxons sometimes referred to the shield as a 'net of spears'). The spears of this period, sharp as they were, would remain stuck in a shield if even a moderate thrust was caught. However, a spear stuck in your shield renders the shield fairly ineffective, but also can render the spear useless to you, so most attacks would have been fended aside using the edge of the shield. After all, it was the owner you had to hit.