Good material for HBP heat spreader

Hey guys, just looking for an opinion on a good material to use as a heat spreader for a heated build plate.

I'm printing ABS or PLA onto a piece of plate glass that I am sure is very flat. Currently this is binder clipped to an aluminum plate that has a silicone heater on the underside.

The issue that im having is that for ABS temperatures (105 C) the aluminum plate seems to warp upward away from the heat source. it took me a while to realize what was going on, because with the binder clips in place the mirror has enough flex in it that it will bend right along with the aluminum.

This is acceptable for my little mendel, but I'd like to scale things up a bit. Not huge, maybe 400x200mm build area. Im concerned that if I use the same aluminum sheet the warp is going to be so large that it completely negates the additional build surface.

So, does anyone know of a good material for a heat spreader? The bed is going to be moving in the y axis, so hopefully it can be as light as possible, just with less warp. I think the aluminum is 6061 T6, which is supposedly heat resistant. Would some kind of steel be better?

Or even if there was a material that warped downward, towards the heater. Then the edges of the mirror would still sit flat and there would just be a small air gap between glass and aluminum in the middle of the plate. the glass is rigid enough that it wouldn't bend downward with the heat spreader...

thanks for any suggestions!!

Aluminum is the standard and I see nothing wrong with using it. If it's flexing, it may be too thin, n=mine is around 4.5mm thick. Mine looks something like this [www.lulzbot.com]

Also it's beed figured out that even with ABS you don't want to go that hot. 80c to 90c is the new standard to prevent shrinkage. Some people say go 100c for first layer then drop to 80c. I myself print at 85c all the time.

Next, you might want a little thicker glass as this will help spread heat and help prevent warping. All of these together may be heavier than what you currently have but it's not too heavy and the standard motors have no issue with this.

Hope this helps.

Use MIC6