Can I use two layers of window film to create a narrow, convection-reducing gap?

Question

This is a follow-up to this question. The official answerer A.I. Breveleri writes:

The ideal separation distance between film and glass is 1/2 inch. Even 1 inch is too thick as it allows the trapped air to circulate freely within the gap. But at 1/2 inch, unless the plastic film is quite tight, it will bow in and stick to the glass over at least part of the window.

A similar question appears here.

I have windows of irregular depth and cannot achieve this uniform 1/2 inch gap. So I was wondering:

1. Could I use two layers of window film, separated by about 1/2 inch, to get close to the ideal air gap?
2. Could I do the same as #1 and also stick a layer of bubble wrap in between those two layers? What would be the effect?

Thanks!

Answer 1

Reducing convection is a minor concern. The benefit described in that answer is trivial compared to the benefit of sealing against airflow through leaky windows. As a proportion of total heat loss, convection is very small as compared to drafts.

1. There would be a benefit to adding a second layer, but not primarily due to convection restriction.

2. A second layer of film adds insulation on its own. I wouldn't clutter your view with bubble wrap, which provides relatively little additional benefit. Because the seal between the first and second layer of film is (presumably) better than the seal between the inner layer and the outside world (due to a leaky window), the net benefit of a second layer is already better than the benefit from just the first layer.

All that said, the savings afforded by a second layer may not outweigh the cost of the product. My advice (having owned older homes in Minnesota) is to do a good job of installing one layer and be happy.