Final answer:
The troposphere is the atmospheric layer that helps insulate the Earth, containing most of the air mass and weather systems.
Step-by-step explanation:
The layer of the atmosphere that helps insulate the planet is the troposphere. This is the lowest layer of Earth's atmosphere, extending from the planet's surface up to an altitude of about 11-13 km (7-8 miles). The temperature of the troposphere decreases steadily with increasing altitude, and this layer contains roughly 80% of Earth's atmosphere by mass. It is where most weather events occur. While the insulation effect is not limited to this layer alone, the troposphere plays a significant role in containing the majority of the air we breathe and contributing to the greenhouse effect that helps maintain the planet's temperature.
All the atmosphere layers including the stratosphere, mesosphere, thermosphere, and the exosphere play parts in Earth's atmospheric dynamics, but for insulating the planet and influencing weather and climate, the troposphere is the most directly relevant.