Summing up, the brittleness may be related to all this things:

1) excessive heating during the moulding process - very likely the biggest reason, and the one we can do less to prevent
2) exposure to direct solar light
3) exposure to extreme climates - hot or cold air
4) exposure to air - oxidation
5) exposure to chemicals - maybe soaps used to degrease the figures speed up the process
6) exposure to other environmental variables - I noticed that figures buried in certain kind of soil are more prone to britleness than other exposed to different soils
7) of course different kind of plastic react in different ways; also bad quality plastics (recycled plastics) may mean brittle figures
8) enamel paints vs unpainted - unpainted figures seem to suffer more, a good thick hand of enamel always helps things to stay put
9) absolute age of the figures, they all will some day or the other become brittle


Things that doesn't seem to affect much the process:
1) acrylic paints - but acrylics have become widespread not many years ago, so maybe we'll have to wait a bit more to see how them affect things
2) play with the figures - you play with them, or you just store them, that doesn't change much, unless it affects some of the above points
3) relative age of the figures - that seem to contradict the former point 9, but we've noticed that elder figures may stay healthy while newer ones may get brittle just after a few years. of course some day all will get brittle, but at the moment you never now which one gets brittle sooner.

Happy modelling to all, and may your figures be un-brittle for many many years in the future

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