I've been making decals for a little while now and ones I have made months ago are still sticking to my windows. You have to use the smooth side (the side that was touching the build plate) and make sure the surface you are sticking it to is clean. Wet with water and place on the window, mirror or shower wall. Overall the lower the shore hardness of the flexible filament you use NinjaFlex = 85A, Flexy = 90A the better they stick. I've found the stiffer stickers SainSmart =98A, Semiflex = 98A, Fillamentum=98A and Cheetah 95A are a little heavier and sometimes they fall off. That said I have a semiflex butterfly still sticking.
I create these designs to encourage people to try out flexible filaments or get some new interesting colors of flexibles. For info on purchasing samples of 6 different types of flexible filament go to flexyfilament.com
Slow and hot works best for flexible filaments.
We developed a great way to distribute cost effective quantities of flexible filament: Splash Spools. A generous amount of filament on a spool with a case so it's not flopping all over the place. Splash Spools store easily in a desk drawer, stacked space or even hang on a wall. Available on www.flexyfilament.com and Amazon. We stock NinjaFlex, Cheetah, SemiFlex, SainSmart, nGen FLEX, FilaFlex and Flexy.