Re: Is it possible to obtain/buy an invisible spray to block/reduce infrared?

Thank you for your question and you are in luck. Not only is there such a 
material, its free (or mostly so). Its water. Detecting infrared 
radiation is detecting the heat signature of the object's surface. Water, 
especially if covering an entire scene, tends to create a single surface 
temperature - washing out contrast. The problem with water is that it is 
only as persistent as the flow of the water over the surface.

Infrared energy is in essence, heat. There is no general correlation 
between an infrared blocking material to its visible appearance. For 
example an invisible gas, CO2, is a strong absorber of infrared energy - 
but only at certain wavelengths within the infrared band. Most infrared 
modifiers are thus going to be tailered to specific bands.

Thus to fully answer the question, I would need to know what part of the 
infrared energy band you want to block. The infrared band goes from about 
1 micrometers (microns) to almost 1 mm wavelength. That's a large region 
to cover. But it may not be necessary to cover the entire band. For 
example, if you wish to block infrared energy from the sun from entering 
a window, one only need block light from about 1 micron to a little over 
4 microns. 

One must also decide what one really wants to accomplish. For example, 
some glasses and plastics will absorb infrared energy. That will keep the 
energy from passing through it, but will increase the temperature of that 
material in the process. Reflective materials will do just that, redirect 
the infrared energy back into space. But most good IR reflectors, 
especially near the visible, are also good visible reflectors - so it is 
unlikely to be transparent. Otherwise one must turn to engineered 
materials - likely to be outside the realm of commercial processes right 
now. Its basicly a zero-sum game. The energy has to go somewhere, 
transmitted, absorbed or reflected. The specific answer is contingent on 
where you want that energy to go.

Some general information http://www.madsci.org/posts/archives/2001-04/988651008.Ph.r.html http://www.wag.caltech.edu/home/jang/genchem/infrared.htm