Wool Pile

The Secret to the Therapeutic Value of Sheepskin

It is the wool fibres, each individually held intact by the tanned skin of the sheep, which contribute to the woolskin's value as a medical product. Interfaced between patient and bed, they reduce pressure, friction and moisture - the primary causes of pressure sores.

Pressure sores are a result of tissue breakdown due to prolonged compression of tissue and the subsequent reduction of capillary blood flow in tissue between skeletal prominences and the body's external environment.

The causes are pressure at susceptible sites, friction or shear forces at the point of contact between the patient and the support surface and moisture or humidity build up at the interface surface.

The unique properties of wool, its high density of soft but springy and resilient fibres, provide a cushion to distribute and relieve pressure at vulnerable pressure points on the patient's body. The wool fibres have a low friction coefficient - they provide a soft and smooth surface to reduce strain on the patient's skin and shear forces on the underlying tissue.

The wool fibres can absorb up to 34% of their dry weight in moisture without feeling damp.

They rapidly dissipate this moisture away from the source - this alleviates discomfort to immobile patients from perspiration and also reduces moisture build up at the pressure points.

Recent Research on Woolskin Properties

CSIRO's Leather Research Centre and industry have collaborated in a research project aimed at identifying the optimum wool pile properties and woolskin type to optimise comfort, performance and durability for Australian Medical Sheepskins.

The results form the basis of the new Australian Standard which will ensure that Australian Medical Sheepskins can be purchased and used with confidence.

Comfort Properties

Comfort trials were undertaken with the help of Concord Hospital, Sydney, to evaluate the responses of elderly volunteers to a variety of wool lengths and fibre diameters in both sheepskins and lambskins (skins from young sheep).

These trials were carried out in a simulated hospital environment to evaluate the comfort properties of sheepskins and lambskins when "as-new" and then after one cycle and 10 cycles of hospital laundering and tumble drying.

Wool pile length, for both sheep and lambskins, was the most important consistent property influencing perceived comfort throughout the tests. Comfort factors, generally related to the softness and support provided by the skins, tended to increase with increasing pile length.

In general, fibre diameter has a minimal effect. The overall comfort rating of sheepskins after the tenth wash tended to increase with decreasing fibre diameter.

In a comparison of skin types, it was noted that lambskins were consistently rated as more supportive but not as soft as sheepskins. However sheepskins were rated overall more comfortable than lambskins.

Performance and Durability

Wool pile performance trials were carried out by CSIRO's Leather Research Centre in real-life studies with patients at Melbourne's Epworth Hospital, and in the CSIRO Leather Research Centre.

Subjective assessments of various properties of both leather and wool were made before and after each cycle of use. The wool was assessed for felting or entanglement, pilling, softness, density and its ability to support a load, and recover.

For wash and in-use performance, lambskins rated better than sheepskins of the same wool length over all fibre diameters. Lambskins suffered much less felting than sheepskins.

In comparison to sheepskins, little change was noted on the lambskins during use.

Conclusion

Whilst sheepskins produce excellent products, the material of first choice is lambskin.

Finishing Sequence

Previously, for the service life of a medical sheepskin, the product was only in "new" condition prior to the first wash. This point-of-sale finish was created by the woolskin tannery which produces a homogeneous ironed finish. Laundering allows the wool fibres to relax - similarly the leather fibres relax and there is a shrinkage on the first wash.

Further laundering does not significantly change the size or appearance of the product.

To eliminate this change from the new to the washed state, the Australian Standard specifies that the wool pile length be fully finished to 30mm at the initial wool finishing stage prior to subsequent wet processing. At the final finishing stage only the extreme wooltips and the long wispy fibres and pills are clipped away from the wool pile. Without further processing the wool maintains the appearance of a washed skin.