The % improvement depends on the window you covered up. If you put it across a single pane window- you have likely halved the heat loss. If it was a poorly fitting single paned window that was drafty, you may have cut heat/air loss through that opening by 80%
Perhaps my understanding on this topic is lacking, but isn't window film usually used to block HEAT from coming in through a window? I didn't know that it had any use in keeping the cold out. That is why when you decide whether or not to apply window film, you have to calculate if the summer heat that you block from coming into your house is greater than the passive solar that you would gain in the winter. This is the idea behind eletrically-charged switch-enabled windows that allow you to change them from tinted to non-tinted at your whim.
Perhaps my understanding on this topic is lacking, but isn't window film usually used to block HEAT from coming in through a window?
Different film. we're talking about the plastic that you double-side tape to the frame to keep drafts out in winter. the summer film is usually a partially reflective thing to keep direct sunlight out and does help some.
the winter film greatly depends on the window you're putting it on, as said above. My house benefits greatly because it's about a million years old with original ill-fitting single panel windows.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
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"You don't get to judge me for how I fix what you break"
Yeh the actual R-rating of the film is like 0.80 or something, hardly worth it if your house is already well-insulated. It does, however, make a double pane window kinda triple pane, like was said, the air that is trapped now there is an extra layer.
But I myself find it most useful to seal up drafty doors or windows (that aren't used), I couldn't tell you what the actual R-rating is for that because it varies with the draft but what I do know is it helps a lot more this way.
Cheap, too, easy to DIY.
Lasts about 2 years if done right and you don't fool with it, does have to be replaced eventually but I like that silly product.
A FE gauge should be standard equipment in every vehicle.