This is a little bit off-topic, but a recent news article (The Walkie Talkie melted my Jag) about a car partially melted by reflections off a curved building is a good reminder that plastic parts are vulnerable to damage from environmental heat. The melted car is an extreme example, but the same thing can happen more easily with PLA parts.
The glass-transition temperature of PLA (Tg) is widely reported as being around 60ºC to 65ºC, although it's been reported that some blends can have a much lower Tg.
As the plastic reaches its Tg, it begins to soften. And when that happens to a finished part under stress, disaster can strike.I've witnessed a RepRap printer that had "wilted" while sitting inside a parked car. Another printer that I saw was a casualty of being in a workspace that was really hot in the heat of summer during the weekends when the air conditioning was left off.
One of our customers had a large and complex multi-part project which experienced a "Dali" moment while being stored temporarily in the garage during the summer.
BTW, the Tg for ABS is 110ºC, much hotter than for PLA, so any parts that are intended to go into a car or other hot environments should be done in ABS.