**4. Measurement techniques**

## **4.1. Pressure sensor/compression-recovery test**

The measurement of interface pressure exerted by a compression device is of importance, for both efficacy and tolerability. Several instruments are available that can be used for pressure measurement directly on the leg. Most of them are air-filled devices such as Kikuhime® (Meditrade, Soro, Denmark; Figure 3a), SlGaT-tester® (Ganzoni-Sigvaris, St. Gallen, Switzer‐ land), and Picopress® (Microlab, Padua, Italy) [35]. They are inexpensive, thin, flexible, adjustable and optimised for different applications and different measuring regimes. Pico‐ press® and SlGaT-tester® allow continuous recording during dynamic tests and over longer time periods. Although direct pressure measurement on the limb is more relevant, there exist several limitations of using *in vivo* measurement techniques. Especially, when comparing different padding performance on a leg, there exist unavoidable variation in application techniques and varying limb movement. Moreover, the location of pressure sensor at the critical sites especially over bony prominence is highly unstable, which may cause unnecessary noise or experimental error. The above facts indicate the need for a simple or alternative method to obtain pressure absorption ability of padding.

Compression load-recovery test is common to obtain the energy absorption ability of a nonwoven material. An Essediel thickness tester was used for measuring compression characteristics of textile materials (Figure 3b). The specimen was placed on a flat surface, and the transverse weight was applied using a pressure foot (20 mm diameter). The compressive pressure was increased from 20 to 200 kPa by applying additional dead weights during the compression cycle, and similarly in recovery the pressure was decreased in steps. The thicknesses were measured at different compressive loads during compression and recovery cycles. The initial thickness *To* was taken for the initial pressure *Po* (~2 kPa), which was due to weight of the pressure foot without any applied external load. The works done during compression and recovery process can be obtained from the plot of thickness versus compres‐ sive pressure (Figure 6). These calculated energies can be further used to characterise padding performance as discussed in detail in the next section.

**Figure 3.** a) A simple prototype for the pressure measurement using Kikuhime® pressure sensor; b) An Essediel thick‐ ness tester for compression-recovery test
