The Design of Nappies

A chemistry worksheet to help students i) understand the design of nappies and ii) design a fair test

This activity could be easily adapted by students to use as a science project.

The Design of Nappies

Disposable nappy manufacturers had to design a nappy.

It had to be soft on the baby's skin, keep skin dry, have a high water absorbency and a waterproof external surface.

They produced the following design.

Nappy

(a) Draw and label a diagram to show a side view (a cross-section diagram) of the nappy layers between A and B.

Outline box

(b) The most important overall property of any nappy is to absorb high volumes of water.

Some students tested the water absorbency of several materials that could be used for nappy padding.

They dripped water slowly onto each material until water started to drip through.

Nappy experiment

For this to be a fair test, name TWO things that should have been kept the same for each material tested.

(i) .........................................................................................................................................

(ii) .........................................................................................................................................

Material	Price	Bio- degradable?†	Water- proof?	Water absorbency‡	Strength	Softness	Water permeability*
Superabsorbent polymer	high	yes, but slowly	no	very high	weak	soft	low
Fluffed cellulose pulp (made from wood)	low	yes	no	high	weak	soft	high
Tissue paper	low	yes	no	medium	weak	soft	low
Woven cotton cloth	high	yes	no	medium	strong	soft	medium
rayon fabric	low	yes	no	low	strong	soft	high
Non-woven poly-propylene fabric	low	no	no	nil	strong	soft	high
	medium	no	yes	nil	strong	hard	nil
Clear polythene sheeting	low	no	yes	nil	strong	soft	nil
Whitened polythene sheeting	low	no	yes	nil	strong	soft	nil

* permeability          = how easily it lets water through
†biodegradable       = whether it will readily break down in the environment
‡ absorbency          = how much water it holds

(d) From this table, which material would be most suitable for a nappy lining that meets the manufacturer's requirements?

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(e) How are the properties of a good padding different from the properties of a good lining?

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