The rubber-hedge euphorbia is a many-branched, succulent plant, usually 3-5 m but may reach 10 m on occasion. The bark of very old specimens is grey and rough with longitudinal dents and ridges that break up into very small fragments. There are sometimes conspicuous, small protuberances, such as bulges, knobs, or swellings, on the bark, and occasionally black, rough, crosswise bands. The branches are cylindrical, smooth and glabrous-green, 5-8 mm in diameter, forming brush-like masses that are the best-known feature of this species. The plants do not have spines.

The leaves are small and slender, up to 12 x 1.5 mm, and are rarely seen as they fall very early. Leaf scars on young twigs form conspicuous dents which contract until they are no more than grey dots on older branchlets; they can even be seen on fairly thick green stems. The thin twigs are pendant (hanging down), pale green, and occur opposite each other, alternately, or in groups on the branchlets, which gives a rather untidy and rounded appearance to the crowns.

The flowers are yellow, inconspicuous, and carried in clusters at the apex of the short branches or in the angles of branches. They appear from September to December.

Fruits are tripartite capsules (divided into three parts), about 12 mm in diameter, longitudinally very slightly lobed, short-stalked (8 mm), pale green, with a pink tinge and conspicuously pubescent (clothed with soft hairs). As with other members, the capsules dehisce while still on the tree. The fruits appear from November to December. The stalks are generally bent at an angle.

The seeds are oval, about 4 x 3 mm, glabrous, smooth and dark brown with a white line around the small white caruncle (fleshy wart near the hilum of the seed). This spineless species contains large quantities of latex which is freely exuded by the twigs and branchlets at the slightest injury.