[ben123]

I can see some logic, as @oberon476 has suggested, that adding window film might speed up the failure of the seal in a sealed unit as one pane absorbs more heat from the film that does the other. What doesn’t make sense to me, though, are these instructions about leaving a gap around the perimeter to ensure “proper thermal expansion”.
“This gap is essential for the proper thermal expansion of the glass….”

Whether 100% or 99.X% (with the edge gap) of the glass is covered isn’t going to make a measureable difference to the heat absorbed by the film and conducted to the surface of the glass.

If the glass was going to expand from the added heat, the extremely thin flexible film that is butted up against the frame isn’t going to impede it.

There is a flexible gasket material between the glass and the surrounding frame to allow some slight movement with temperature change (and that is mostly to protect the glass against thermal movement of the frame).

Glass has an extremely low “coefficient of thermal expansion”, meaning that it expands and contracts little with temperature change. As an example, a 36” wide sheet of glass would need to undergo a 350F temperature change before it would expand enough to make the 1/16” edge gap disappear (but there would be a gap on either side of the window, so double that).

I think the thermal expansion mentioned may be for the film. If the film expands and there is no room the edge may bump up and allow dust under. For blackout, there is a white both sides that doesn't seem to hold as much heat as the black.

 

[ben123]

I was able to install the film. Thanks to everyone for the advice!

I'm thinking about using some sort of tape to cover up the gap at the edges. Does anyone know of a tape that blocks out light but is easy to remove and leaves little residue?

I'm thinking about brushing some kind of lubricant on the window frame itself, then using white silicone caulk to cover the gaps. They mentioned electrical tape above but I think that will wilt in the heat and leave a gooey mess. Did you find something that will work better?