The heating of the Felix's heatbed was very slow and it refused to go higher than 88 degrees. I added an isolation sheet made with a piece of cooker hood filter, and attached with 3D-printed clips. Now the bed heats up to 100 degrees without a problem.Cut out a sheet of cooker hood filter of 25 by 30 cm. Follow the plan in the SVG file for the holes for the mounting screws and cables. Unmount the heatbed by unscrewing the 3 nuts at the bottom. Take care not to loose the washers and the springs. Position the isolation sheet and put the 3 screws through the holes. The two ends in the middle at the right side can be fixed together with a piece of tape. Screw the nuts back on and recalibrate the table. Print the clip 5 times, and attach 3 of them at the left side, one at the front and one at the back.