I've tried to put some reflective metal on the bottom part of my bed. The results were disasterous. You can observe my broken glass on the picture. This happened twice, that's why i abandoned this idea. Sorry moyboyufl. But heating itself were more effective I think. Temperature probably have been raising much faster, what was the reason of broken glass.

I have never thought about emulate the toaster, but yes - my bed look very similar. I have chosen the easiest way to make hot bed, i.e. glass which is flat for sure. I couldn't find good aluminum plate, that is why I've mounted glass only. Also the resistance wires were pretty easy for me to get/buy. I have been looking for resistors but I've failed to obtain proper ones. To prevent the melting... yes I had to tape the bottom and the frame with insulating tape. The glass is also taped from the top.
Thanks for your tips moyboyufl. I will probably use them during next maintains.
For now, my bed works and as the thermistor shows, it allows me to reach 120 degrees. What is more, I can easily set the bed parallel to the head, which was problematic which my previous solution - hand made frame of textolite.

Are you trying to emulate the radiative heating of a toaster? If so, be aware that radiation is orders of magnitude less efficient Than conductive heating. Are you trying to heat the bed or the part directly. Either way, you should cover the wood on the bottom with a reflective metal. Foil is a start but the more reflective the better. If you are trying to heat the bed, I'd suggest using an aluminum bed painted black on the side of the heat. Using just glass will probably just let the radiation pass through, depending on the type of glass. You can test this out by putting your hand a few inches from glass to sew if you can feel the radiation. The glass will be heated by convection, which is the moving air around the coils touching the bed, so you'd probably want to insulate the bottom to trap as much heat as you can without melting your printed coil holders. If radiation is your main heat transfer method, you might find mixed results with different colors, black being the most effective. I'm really curious to see your results. Good luck!