I've used my new SeaToSummit Ultralight pad a few times in my hammock in cold (freezing) conditions. It's 5cm thick and is insulated (R = 3.1) with 2 forms of insulation: 1) a heat reflective coat; 2) synthetic insulation. My pad is the Regular size and is mummy shaped. It's got a clever design where the stuff sack also contains a grey inflation bag (see photo). This inflation method is useful to reduce moisture build up inside the mat from breath. The mat weighs 480g (17oz) and is 183x55x5xcm - pretty light.

How does it work in practice? It inflates easily using the bag and is comfortable in the hammock. A key feature is how flexible it is because of its "air cell" design - see the photo where it bends over a pillow.
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I have a dual layer hammock that helps to hold the mat in place. It's not very wide at the foot end but with practice I'm getting better at positioning the mat exactly where my feet and legs are in the hammock. I've been warm all night with it and am impressed with the insulation. Deflating is easy. Getting it back into its bag is trickier when you don't have a clean, flat floor to roll it on! This is because it gets folded in 3 lengthwise (normal practice) before rolling. But I've managed to re-fold it or taken it back in a rolled but unfolded shape.

Finally, what I really like is its flexibility: the way it can cope with hammock or tent camping all year round in my local conditions.