Its pliant branches give it the common name "limber" and specific epithet flexilis. Its long needles are a dark, blueish green, its bark is heavily creased and dark grey. Its pale wood is lightweight and soft.

Pinus flexilis is typically a high-elevation pine, often marking the tree line either on its own or with whitebark pine (Pinus albicaulis), either of the bristlecone pines or lodgepole pine (Pinus contorta).

In favourable conditions, it makes a tree to 20 meters (65 ft), rarely 25 meters (80 ft) tall. However, on exposed treeline sites, mature trees are much smaller, reaching heights of only 5–10 meters (15–35 ft). In steeply-sloping, rocky, and windswept terrain in the Rocky Mountains of southern Alberta, limber pine is even more stunted, occurring in old stands where mature trees are consistently less than 3 metres (10 ft) in height.