The string, according to Ascham, "though it be little, yet [is] not a little to be regarded." A short string might snap the bow and a long string might be snapped by the bow, to the bow's detriment. Also the string must be set on straight (nocked correctly) lest one end twist differently from the other during a shot, possibly torquing the bow and breaking it.
Ascham tells us that a good string is made of "good hemp, as they do now-a-days, or of flax, or of silk," then goes on to tell of fanciful sounding materials used "in old time." Sir John Smythe, the great Elizabethan champion of the longbow, writes, "and the strings being of very good hempe, with a kind of water glewe to resist wet and moisture; and the same strings beeing by the Archers themselves with fine threed well whipt, did also verie seldom breake. But if anie such strings in time of service did happen to breake, the soldiers archers had alwaies in readiness a couple of strings more readie whipt and fitted to their bows to clappe on in an instant." Philip D. Hartley, writing in the Journal of the Society of Archer Antiquaries, postulates that "English Hemp" came primarily from the common stinging nettle. Nettles are related to ramie, which Tim Baker finds to be the strongest of natural fiber bowstrings.
In The Traditional Bowyer's Bible, Baker says that, with a little practice and a drop spindle, one can spin enough fiber to produce a bow string in about an hour and a half. A starter thread is tied to the spindle just below the weight and fed through the notch. Enough raw fiber is teased out to lay over the starter thread. The two are twisted together and the spinning begun. "Pulling the threads from the bundle before you need them," he says, "is the secret to fast, uniform spinning."
How the spun hemp was made into a bowstring is a mystery, as there are no surviving bow strings to show us. We pattern reconstructions on the "traditional" Flemish string, as its design appears most likely to have come out of a medieval bowstring-making tradition. Tim Baker provides details on producing several "Flemish" strings in The Traditional Bowyer's Bible.
Whipping (modernly called "serving") involves winding thread around the loops and center section of the string to protect it from wear.
A "fitted" string is one made to the measure of a particular bow, with loops at either end. Where string cannot be matched to bow, a single loop serves better. In such cases, the non-looped end is tied to the bow using a timber hitch. This method allows string length to be adjusted and the bow to be braced correctly.
Arrow nocks from the Mary Rose suggest that the strings were 1/8 inch in diameter, although this may reflect the somewhat larger diameter of the "whipt" section.
Ascham says, "When the string beginneth never so little to wear, trust it not, but away with it; for it is an ill-saved halfpenny, that costs a man a crown."