The most efficient way to stay warm is to increase or decrease the insulating factors.
Putting on or taking off a garment (when we say "dressing in layers") serves to create cavities that retain heat without dispersing it.
The research on “smart textiles” continues in a very encouraging way: a small research team has developed adaptive clothing, textile materials that could drastically change the way we dress. The idea of adaptive clothing is to develop a material capable of "increasing" its insulating properties by reacting alone to the environment and modifying its configuration by adding or subtracting "insulating" space to provide for body thermoregulation without modifying the clothing .
The initiative belongs to a research field funded by ARPA-E, an incubator agency of the US Department of Energy. ARPA-E since 2009, it has been funding the most promising fields of research on energy sustainability and improving the performance of fabrics, construction materials and products.
To put it simply, to say that we will have "adaptive clothes" is to say that we will have sweaters that become jackets, and perhaps shoes that become moon boots: yes, I know, don't laugh.
In other words, it is all too simple, but mind you, that is exactly how it could go.
The images of the prototype in action speak for themselves.
To find out more: https://arpa-e.energy.gov/?q=slick-sheet-project/passive-thermo-adaptive-textiles