Have a look at a material called Topas. Google will be useful.

Cheers

Politicians like to panic, they need activity. It is their substitute for achievement.

I appreciate the lead Pud!
I acquired the transmission characteristics from the manufacturer. Unfortunately the IR spectrum for TOPAS is also very limited in the 7-14 micron range - see below.

Found this. This article that goes with the graph requires payment: https://pubs.rsc.org/en/content/articlelanding/201.... In general, trying to get Vis/LWIR is not a cheap endeavor.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

Your transmission % will drop significantly with thickness as well. The materials in the graphs IRstuff provided are only 10um thick films. What thicknesses are you considering?

I had noticed yes. I will need a thickness significantly larger than this. As this will be applied as a protective window I will likely need the sheet to be 1/4" to 1/2" thick depending on the other characteristics of the polymer.

Huh? What material is your window?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

I am attempting to find a suitable material. As mentioned in the original post, I have tested materials such as PC, acrylic and PETg.

NVM, your wording misled me. I think you should just stick with the usual suspects, like Cleartran and ZnSe

A polymer vis/LWIR material is the holy grail of infrared; unlikely you'd just stumble across it on the internet. Most applications requiring vis/LWIR are sight windows for power boxes or reactors, and protection is in the form of metal meshes or windows

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

It would be great if all the lab guys could chuck out their sodium chloride IR discs...

Lol well I appreciate the input!

I saw this company (link below) had developed a polymer window for visible and IR freq transmission and I wasn't sure if this was made with a more prevalent material that I had just not come across.

https://www.iriss.com/emsd-cast-products/cap-serie...

In order to be transparent the spacing of the atoms needs to be right. It seems to me that in the jumble of molecules in polymers that it is less likely than in more regular materials to have a uniform transparency across a range. Ref https://www.scientificamerican.com/article/what-de... and https://physics.stackexchange.com/questions/7437/w...

Which is why sapphire and germanium are popular IR window materials and I expect that polymers are not.

I am dubious about the IRISS product because the FLIR camera is being used to look through what appears to be an open mesh, but I suppose if the material is thin enough and protected by a sturdy steel frame then it will be transparent enough for very short range measurements.

Interesting; a few of the pictures appear to show something that actually a bit cloudy, kind of like PIR motion sensor window material, but unclear what the picture was supposed to show.

Their literature mentions "polyolefin" as the their material. https://www.iriss.com/resources/TB006.pdf

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

Polyolefin is about as close as you're going to get- polyethylene has just a few peaks, just like Nujol (paraffin oil used to make "mulls" so you can do IR spectra on salt discs).