A printable 3-layer foldable gift/money/message/postcard/foto envelope.
Once printed, fold them around what you want to give and close with the printed lip.

* For a version with an added rose or heart as decoration (also without text) see the remix.

I added 3 formats:

Create stunning visuals using top fill patterns in the slicer and dual color PLA. (the top of the print becomes the outside of the envelope)

Note: to print properly, on the 2nd and 3rd layer the folding areas (created by bridging) must follow a fixed direction! Normaly the slicer would do this correct because of the bridging, but you can also look at the attached screenshots of the slicer how you can check it.

Because it is only a 3 layer print (excl. the lip), make sure you have good bed leveling and good bonding between layers.

Print in PLA, nozzle 0.4mm and layer height 0.2 (also 1st layer!)
Do not scale or use other layer thicknesses, otherwise the fold lines will not work properly.

________________________________________________________________________

Used infills and PLA:

Purple (small) envelope: Octagram Spiral with Blue - Red magic PLA

Green (middle) envelope: Archimedian Chords with Green - Blue Chameleon PLA

Gold (big) envelope: Concentric with Silver - Gold magic PLA

________________________________________________________________________

Folding

When folding for the 1st time, bend the parts to be folded back and forth several times to make them move smoothly. (Do it carefully, and bend only the fold line, after all it's only 3 layers..)
Now you can add something and close the envelope by hooking the cover with hole over the button..

Special Thanks

Special thanks to Dave Antonacci at Thingiverse to challenge me after seeing my Postal Xmas Kitcard asking:
"where's the 3D-printed envelope? The postal service might not accept one, but it would be nice for "wrapping" small flat gifts, like pictures or gift cards."

FilamentStories made a short of the model! 

* Due to the use of only 3 layers, it is important to guarantee the strength of these layers by printing at least 2 layers crosswise. Therefore I would not recommend using an infill pattern on the bottom layer as well.