OK, its my first post.  I’ve been reading as much info as I can, but I need a solid answer before I drop some dough.
im building my first FTIR surface, and im going to start big!  I want to make something big (40x30)
So what thickness should I be looking for so I dont get any bending?
And while I have your attention, do you know any links where I can find a good way to attach the IR Bulbs

Get 1/2” acrylic if want it to be stiff.

There’s a lot of info here about mounting LEDs. Use the search function and you’ll find a ton of info on just about anything MT.

I mounted my LEDs in an aluminum rail, as most builders do.

thanks for the quick response!
Ive been searching google for a place to buy aluminum rails with no luck.  Is this something that home depot or lowes would have?  And also, if i am mounting the acrylic so it is fastened down on all sides, should it still be thick?  or will 1/4” be ok if it is secured really good.

Most hardware stores carry the aluminum.

1/4” inch will work fine. You ‘ll just notice some flex when you lean on it.
Could you break it? Maybe if you sat on it really hard.

To help with ir light leaks with the aluminum rail i found that the LED holders work really well. They also help to give you more space between the acrylic and the LEDs.

... and they look way cooler!
Those are sweet. I used adrop of CA glue. It works, but your holders are very sanitary. Well done.

szadkowski, Where’s a good place to get Led Holder?

will the actual color ( black ) of the LED holder absorb any IR ?? kinda like a football player putting black under his eyes to reduce glare.