Yumis are exceptionally tall (standing over two meters), surpassing the height of the archer (kyudoka). Yumis are traditionally made of bamboo, wood and leather using techniques which have not changed for centuries, although some archers (particularly, beginners) may use synthetic yumi. Yumis are asymmetric; the upper and lower curves differ and the grip is positioned at about one-third the distance from the lower tip.
The string (tsuru) of a yumi is traditionally made of hemp, although most modern archers will use strings made of synthetic materials such as Kevlar, which will last longer (around one-thousand shots). Strings are usually not replaced until they break; this results in the yumi flexing in the direction opposite to the way it is drawn, and is considered beneficial to the health of the yumi. The nocking point on the string is built up through the application of hemp and glue to protect the string and to provide a thickness which helps hold the nock of the arrow in place while drawing the yumi.
Serious kyudo archers treat yumis with reverence; as pieces of great power and as teachers with much to impart to the student (yumis are said to hold within them part of the spirit of the person who made the yumi). A kyudo student will never step over a yumi which lays on the ground (that would be considered disrespectful), and will typically treat a yumi as they themselves would wish to be treated (e.g. kept away from excessive heat or cold, kept dry, kept away from excesses of humidity or dryness, carried upright). It is also considered disrespectful to so much as touch another person's yumi without his or her permission; yumishi (yumi-maker) Kanjuro Shibata, Sensei has said this is like touching someone's spouse.
Bamboo yumis require careful attention. Left unattended, yumis can become out-of-shape and may eventually become unusable. The shape of a yumi will change through normal use and can be re-formed when needed through manual application of pressure, through shaping blocks, or by leaving it strung or unstrung when not in use.
The shape of the curves of a yumi is greatly affected by whether it is left strung or unstrung when not in use. The decision to leave a yumi strung or unstrung depends upon the current shape of the yumi. Yumis which are relatively flat when unstrung will usually be left unstrung when not in use (yumis in this state are sometimes referred to as being 'tired'). Yumis which have excessive curvature when unstrung are typically left strung for a period of time in order to 'tame' the yumi.
A well cared for yumi can last many generations, while a mistreated yumi's usable life can be very short.