These are insulation covers for the aluminium "wings" of the Simple Metal heated bed upgrade, to reduce heat loss.
After installing the heated bed, I noticed that the black “wings” got quite warm, they acted as heat sinks and radiators, even with the delrin pieces in the kit that were supposed to insulate the “wings” from the machined print plate. It probably has some effect, but a lot of heat is lost that way still.
It seemed like a good idea to put covers over the wings to reduce the heat loss. I did that by designing hollow PLA wing covers. They are designed as solid parts, but printed with “hollow” infill and 0.8 mm skin. The parts should be hollow since air is a good heat insulator.
With the insulation I can reach 60C bed temperature in 4-5 minutes and 100C in 19-20 minutes.
Note that the photo shows a small rectangular hole on the left which is not in the uploaded model. The large rectangular hole is to allow access to the X belt tensioner. The smaller rectangular hole was not required and therefore removed in the model.
Print the STL file with “hollow” infill and 0.8 mm skin. The parts should be hollow since air is a good heat insulator. They can be printed with PLA.
If you for some reason have an issue with the fit, an OpenSCAD is included.