Soft

The air is full of fluffy seed at the moment. The main culprits seem to be Purple Loosetrife and Thistles which are abundant near where I work.

Softness (or hardness) can be quite a difficult thing to measure as it seems to be arbitrary - see any online cycling forum on the subject of saddles for example. But it can be done.

The Mohs scale measures the hardness of minerals but is a fairly simple scale, rating minerals depending on whether they can be scratched by other minerals eg, talc (1) can be scratched by Gypsum (2) which can be scratched with a fingernail (2.5). It is not linear so that Corundum at 9 is twice as hard as Calcite at 8 but Diamond at 10 is four times as hard as Corundum.. Confused yet?

Softness is measured on an even more simple scale with the usual ratings being that of thistledown, kittens and babies bottoms. I am not sure what happens if you try to scratch a kitten with thistledown or a babies bottom (or variations thereof) as I haven't tried it but perhaps a softness scale similar to the Mohs one could be invented?