What is Viscose and Modal fabric?
Viscose and modal are made from plant material
That's right, viscose and modal are made from plants, typically trees, but it could be soybeans, bamboo grasses, or even cotton plants. They are all variations of the same fibre generically known as viscose in Europe and rayon in North America. Scientifically they are described as regenerated cellulosic fibres. That means they are composed of cellulose (a compound which gives plants their stiffness) that has been extracted, dissolved and then realigned to make a fibre. So, despite being man-made, the fibre itself is composed of long chains of cellulose molecules that have been lined up to make a useful filament (very long continuous fibre), not unlike silk. This plant-based chemical structure is what gives these textiles their desirable properties, such as a natural next-to-skin softness, breathability and good moisture management.
Does that mean these fibres are synthetic, like nylon or polyester?
No. Viscose fibres may be man-made, but chemically they are still plant-based and therefore not synthetic. That's what sets viscose apart from nylon or polyester, both of which are made from petroleum derived compounds that do not naturally occur and are therefore fully synthetic. Synthetic fibres do not have the same breathability or moisture management properties, which is why they have quite different uses. Why? It comes down to the chemistry of the base compounds and how they react with water.
The naturally occurring cellulose compound is attractive to water (they are said to be hydrophilic). Water molecules 'wet' the fibres and even penetrate into micro pores inside the fibre structure. This is why viscose and modal are all water absorbing fabrics. This affinity to water (and water vapour) is what helps to make these fabrics so breathable.
In contrast the compounds that are used to make nylon and polyester are not attracted to water (they are said to be hydrophobic). In just the same way that oil won't mix with water, nylon and polyester fibres don't attract water molecules. Instead of 'wetting' the fibres water pools on the surface of the fibre with no internal penetration. This gives nylon and polyester very different properties: these fabrics are excellent at wicking moisture away precisely because the water stays on top of the fibre. A close weave will also trap water, water vapour and heat making some nylon or polyester fabrics hot and clammy to wear (an experience you won't forget if you ever had to wear a cheap Polyester uniform on a hot day).
So they are all fairly similar then?
Yes. Viscose and modal are very similar – so much so that you might be forgiven for calling them all viscose. The important thing to remember is that they may be man-made but they are not synthetic. In fact, as fibres that are man-made from a natural product, we might call them semi-synthetic fabrics.