In this test I wanted to compare different filaments on how well they could be used as a spring under constant tension. 

For my test I used the following filaments:

.) TPU Overture TPU high speedFlexible TPU Filament

.) Nylon CREOZONE Top Quality Brand 3D Printer Filament (Nylon White)

.) PETG Prusament PETG Prusa Galaxy Black

.) PLA Noulei Temperature Change 3D Printer Filament

For the spring model I used Parametric Bobblehead Springs by 3D Printy | Download free STL model | Printables.com with the following settings:

I did some tests beforehand and determined I could:

.) Extend/Compress Springs with 1.6 mm Weight from around -30 % to + 30 % of their original length for a short amount of time without permanent deformation.

.) Extend/Compress Springs with 0.8 mm Weight from around -40 % to + 40 % of their original length for a short amount of time without permanent deformation.

For comparison a metal spring I tested extended for more than 230 % of it's original length. For this experiment I used the thicker 3d printed springs with 1.6 mm Weight because I thought they could have a higher chance of retaining their original length. PLA & Annealed PLA Springs had the highest Strength, PETG & Nylon were a little bit weaker, TPU had nearly no strength. All test samples were screwed to a piece of with and extend from 10 cm (original length) to 13 cm and left for 8 hours at 25-30 °C.

Final results show:

.) PLA showed the worst performance out of the test subjects

.) Annealed PLA broke after a few hours. (Broken parts still longer than original length)

.) TPU & Nylon performed about the same

.) PETG performed the best but still deformed by about 5-10 %

My conclusion is that no filament I tested can be used as a spring which is under constant tension or compression. I ran into the same problem trying to design this model Fully 3D Printable Push Latch Mechanism [WIP]. I could imagine that different print settings may change the output by a little but would not make a drastically difference. Reading about this issue I saw that HDPE should perform well regarding deformation under constant stresses. The Fall and Rise of HDPE 3D Printing Filament. I couldn't find any HDPE filament on amazon and it looks like a nightmare for printing. 

So, my recommendation is to use metal screws. Either buy them in a set BGS DIY 9806 | Springs Assortment | Compression Springs | 246 Pieces | in Assortment Box : Amazon.de: DIY & Tools or make them yourself How to make springs - YouTube.