Manufacturer's Ratings for outdoor gear should not be taken too literally, without considering the following - every manufacturer of outdoor gear wants to outdo the competition, and the following factors are important to consider. Ratings are measured by the manufacturer, so there is presently no consistent standard, however, a new Rating standard is being introduced: ASTM F3340-18 which will become the standard Rating for Insulation.
When hammocking, insulation is required ‘under the body', and air-mattresses perform at their peak with full-pressure. With falling air-temperatures from daytime to nighttime, there will be a corresponding reduction in air-volume, causing a lowering of pressure inside the air-mattress.
Depending on the season and ambient temperature, it is important to check your air-mattress pressure at night-time. Body weight has the potential to compress low-pressured baffles, causing loss of body heat, and it is important to ’top-up’ the baffles before climbing in for the night. Using an electric pump to initially fill baffles is fine, but the ‘top-off" must be done with breath-work, which is more powerful than a portable pump.
Down products compared to Fibre products, are generally warmer but also more expensive. Do your on-line research, or shop in a reputable store which employs experienced staff familiar with products sold.
Down is the term referring to the fluffy plumage found under goose or duck feathers. Pure Down has a high-loft (thickness) ability, and compresses to a smaller volume than synthetic insulation. The biggest failure with Down is it collapses when wet, but a lot of R&D is continuing to process Down with a protective water-proof coating. Low-grade Down contains varying amounts, from low to high percentages of ‘feathers’ to keep the price down, but may still be sold as Down, so do your research.
Fibre is a manufactured synthetic (plastic) polyester, heavier than Down. Hollow-fill Fibre is lighter and warmer than standard Fibre, gram per gram. The big advantage with Fibre is, it doesn't collapse as much as Down when used for under-body insulation to sleep on. Some sleeping bag manufacturers use Down for top insulation, with Fibre used under, the advantage is offset by the extra weight - so good advice is required to avoid disappointment before experience is gained.