## BLOG 4: What is the elasticity of a bandage? What are the differences between extensibility and elongation?

In previous posts we have discussed the different characteristics of a bandage, among which is elasticity. Speaking generally, elasticity is: “the ability of a material or substance to return to its original shape, size and condition after it has been stretched.”

**How is the elasticity of a bandage calculated?**

Elasticity is the property of a bandage to stretch and return to its original position after the force that stretched it has ceased to act. The elasticity of a bandage gives it the ability to deform to form a bandage in an area that is uneven in shape, such as the elbow or knee. In this way, a bandage, thanks to its elasticity, can modify its length at different points of the area where it is being applied.

If a bandage were made of an inelastic fabric, there are regions where there would be folds, since in areas of complex shapes it would not adapt itself correctly. In contrast, an elastic fabric can change its length and adapt itself depending on the needs of the shape.

Figure 4.1 Prepared by Carlos Izquierda S.L.: Initial position; stretched long-stretch; stretched short-stretch

The way to calculate the elasticity of a bandage in Europe is given by EN 14704-1:2005 which is calculated by the following formula:

Figure 4.2 British Standard BS EN 14704-1-2005 Determination of the elasticity of fabrics (BSi)

S (%): Elasticity of the bandage in %.

E (mm): Maximum length in mm after stretching it to its maximum extension 5 times

L (mm): Initial length of bandage in mm without being stretched

From here we see that the elasticity is measured in percentage (%). For example, using a bandage of 5 meters initially and without stretching, if after the five cycles of maximum stretching it has a length of 10 meters, the elasticity of the bandage would be 100%.

**What is elongation? **

When we talk about the elongation of a bandage, it is exactly the same as elasticity. Analyzing the European standard DIN 53504, this is confirmed. In fact the formula for the calculation of elongation is the same as for elasticity.

So when we talk about the elongation of a bandage or the elasticity of a bandage, we are referring to the same thing.

**Extensibility of a bandage**

Technically speaking, the extensibility is the property of the bandage to stretch to the point of rupture, hence its extensibility will be given by the point before that rupture occurs. But we must be careful since there is a clear difference between this and elasticity. While elasticity means the stretching and the return of the bandage to its usual position if there are no forces that stretch it, extensibility is not the same thing and only involves the maximum stretching capacity.

This is due to the fact that from the point of maximum elasticity to the point of maximum extensibility the bandage deforms and does not return to its original position even if there are no forces applied to it. If the maximum elasticity is exceeded by 10%, this is not recovered and the bandage without forces applied will have 10% more length. In other words, once the maximum point of elasticity is exceeded, extensibility begins, and it does not recover its original shape. The extensibility is measured until the fibers break.

In any case, these are technical and theoretical definitions; in everyday life, it is common to refer to elasticity, elongation and extensibility as synonyms.

No mention has been made of how to classify bandages according to their elasticity. As a simplification, since there is no consensus on the matter, a possible classification would be as follows:

- Inelastic bandages: elasticity < 10%
- Elastic bandages: elasticity >10%. Within this category we would also have:
- Short-stretch bandages: elasticity between 10% and 100%
- Long-stretch bandages: elasticity greater than 100%

However, as we have just mentioned, this is only an approximation based on the categorization made in the European standard DIN 61632 “*Verbandmittel*” (1985).

Figure 4.3. DIN 61632 Verbandmittel. Idealbinden

To conclude, it is worth mentioning that no reference has been made at any time to the compression of the bandage. This is because the elasticity of the bandage and the compression it exerts depend on other factors, as we will see in future posts on compression.

*Prepared by the technical department of Calvo Izquierdo S.L.*

*with the collaboration of Carmen Alba Moratilla*

__Bibliography:__

*https://www.collinsdictionary.com/dictionary/english/elasticity**British Standard BS EN 14704-1-2005 Determination of the elasticity of fabrics (BSi)*__http://oa.upm.es/38763/1/Manual_%20textiles2021.pdf____https://www.sciencedirect.com/topics/engineering/stretch-bandage__*EN 29073-3 look for this standard. It is the test methods for textiles and you will find useful information.*-
*DIN 61632 Verbandmittel. Idealbinden. Berlin, Wien, Zu**̈**rich: Beuth Verlag; 19* -
*Partsch H, Clark M, Mosti G, Steinlechner E, Schuren J, Abel M, et al. Classification of compression bandages: practical aspects. Dermatologic Surgery 2008;34(5):600-9. [PUBMED: 18261106]*