The main differences are:
1. G2 has a polyester hammock as well as polyester bag. With the G1 we saw that the nylon hammock would stretch over time, which resulted in some sleeping bags ripping. (12 warrantied, out of 600 sold) so we decided to change to a polyester hammock.
2. Higher quality polyester on the sleeping bag (170T instead of 190T), it's quite a bit softer and more durable)
3. The stuff bag is attached to the hammock, it's great for storing your phone or flashlight.
4. Increased the gap between the hammock and sleeping bag, adding that extra pocket of air.
Once we're out of the G1 we don't plan to re-order.
Nylon and polyester are both synthetic fabrics. Nylon also tends to be more durable and weather-resistant, which is why it is more likely to be used in outdoor apparel or gear. Both fabrics are flame retardant, but nylon is stronger, while polyester is more heat-resistant.
In all of our tests we haven't be able to see a single downfall using Polyester instead of nylon. The only difference we've experienced was Nylon has a bit more stretch. But we didn't try to set it on fire or anything either.