Great question! Here is what your Course Prep Manual has to say, which I would agree with:
LIGHT SLEEPING BAG: Synthetic or down, 30-40 degree Fahrenheit rating. Down bags last longer, are lighter, but require more maintenance (and don’t do so well in wet weather). It is also essential that if you do get a down bag, you line your stuff sack with a plastic bag. Compared to down bags, synthetic bags are bulkier, but they are a lot more economical and you can stay warm in a synthetic bag even if the bag is wet. We recommend a compression stuff sack for packing your sleeping bag, especially for synthetic bags. Students in the past have recommended only bringing a sleeping bag liner and reported mostly using their liners as we are predominately in warm temperatures.
Having the perfect sleeping bag isn’t so important during the summer months, since the weather will be pretty warm. If you’d rather just bring a liner, any made of silk/synthetic material should be fine. If you tend to be cold at night, you might want to bring a sleeping bag just in case, and if you tend to be hot at night you might opt for just a liner.
I hope that’s helpful!
Nick and the iTeam.