We have did our share of testing with FDM printers and over the years it’s been a push pull of settings.   We wanted a strong piece that was efficient and cost effective.  For strength most of us target a higher infill.  What we found is at 20% infill it seems to give the print strength, but! Even at 20% when it comes to little pokey things on the piece the infill might not line up with small protruding things like mushrooms, bulbous fungi, branch, roots and vines etc. Many times they can be hollow and break off on impact.

After much testing found with a thick exterior shell the protruding things are much more resilient to impact.  This also means with the thick shell we can lower the infill and lower we did!  We took it to 5%.   The prints feel hollow and light weight but those tiny extremities are stronger. 

Here is our current FDM printer settings. 

.10 layer height 
.9 top shell thickness
.7 bottom shell thickness
5% infill