Isfahans are hand knotted on a vertical loom using a Persian knot and very high densities ranging from 160 to 400 knots per square inch. Silk Isfahans have densities approaching 600 knots per square inch. The warp is often made of cotton and the pile is always closely cropped, usually wool and silk. More often than not, silk is utilized in the decorations to heighten the visual effect of the carpets, bestowing on them a certain gleam.