I have just tried my DIY 1.0 oz Monolite hammock for 30 minutes hang during a warm sunny day (75F). It seems to be perfect for a hot day/night. But what if it's colder (down to below freezing) and underquilt is required? Are there any advantages/disadvantages of using 1.0 oz Monolite hammock with a down underquilt?
Not so much. It is fairly helpful to be able to see your UQ through your hammock to see exactly how it fits while inside, but it’s hardly necessary. The hammock fabric is not going to influence your total insulation value enough to concern anybody. Since your body weight is pressing the fabric right against your skin and stretching it out, you are really ruining any chance it has to trap heat.