[cstross]

If stuck to posters or wallpaper it also leaks oil/plasticizer over time (months to years) which is absorbed by the paper and causes staining. I discovered this the hard way in my late teens/early 20s.

Solution is to apply some Sellotape (Scotch tape) to the back of the poster first, then put the Blu-Tack on the plastic tape, which blocks the solvent. And avoid using it on wallpaper (emulsion or gloss paint is fine). Better still, use poster holders and a picture hook, or go the whole hog and frame your artwork properly.

Sugru ... air-cures: it doesn't have the solvent-leaching problem, but if you used it on a poster the only way to get the poster down would involve a chisel or sandpaper. Blu-Tak is for temporary attachments; Sugru is intended to be permanent.

[weavie]

It will also stain the wall and sometimes pull the paint off if left on for long enough.