It is very very cold right now here in Germany - a high pressure system coming in from Siberia.
I measured minus 8,4 centigrade noon temperature - that is -18 Fahrenheit.
So I took my band test system outside, stretched the bands and let it sit for 30 minutes or so.
The bands lost ALL flexibility! No more rubber like behaviour. I saw the "wrinkled" look I noticed a year ago after shooting a sling-x-bow out in the cold.
About five secs of the heatgun restored the rubber in full.
This is one more proof: Rubber stores all of its energy thermally. You stretch out a band, it warms up. Release it, it cools down. Cool it down while stretched, and the stretchiness decreases. Cool it down low enough and there is no more stretchiness.