Compressibility
The Mira HD packs into a fairly small package with a less than average amount of effort. Given the lack of loft, this is not a surprising result since less lofty bags tend to pack more easily.

Warmth
Therm-a-Rest relies on its integrated sleep system and features zoned insulation to keep more loft on top and less (next to none) on the bottom, with the strategy being that the mattress insulates its users. I find the insulation of a sleeping pad never matches up to down fill at the bottom of the bag and usually find sleep system bags cold. However, Therm-a-Rest has done a good job of compensating for the lack of insulation on the bottom of the bag with a 750+ down fill (using Nikwax^TM hydrophobic down that repels moisture, improves loft and dries faster), ThermaCapture^TM lining  (intended to reflect radiant heat back to your body),a less roomy (and therefore less drafty) bag, and the Toe-Asis^TM foot warmer pocket.  Users found the bag generally warm but getting beyond its limits when temperatures dipped into the high 20s.

Features
The Mira HD has a women’s-specific differential cut but it ends up being a little narrow overall. The bag has a draft collar and full-length zipper draft tube, cinchable hood and external zip pocket. The hood was extremely comfortable and the external zip pocket roomy enough for multiple items such as a music source, earphones, tissue, headlamp or any number of items one would find desirable for easy access. 

Although Therm-a-Rest advertises a snag-free zipper, there is no stiffening tape on the inside and users did find the zipper to snag quite easily.  

The Mira HD also introduces Therm-a-rest’s patent-pending Toe-asis™ Foot Warmer which is a baffled pocket of insulation in the footbed. Feet can actually be slid inside this footbed to maximize warmth, but can also be kept out if that is more comfortable and still have the benefit of the insulation. I found the foot warmer too constrictive but other testers thought it was a unique and useful feature.

The SynergyLink^TM Connectors are provided to secure the sleeping bag to a large 25 x 77 in mattress, and very easy to use. Using the straps require one to “move within the bag” rather than having the bag move with you. Because the bag is already restrictive, active sleepers may choose to dispense with the use of them (as I did). The straps are detachable and can be easily removed if you feel the same way. 

Overall Comfort
The Mira HD is a rather square and narrow bag (even if it is shaped with the female figure in mind) that does not conform to a woman’s body. The lack of space undoubtedly contributes to its warmth but does less for overall comfort, particularly for those of us who move frequently during sleep. The narrow footbed also restricts movement, particularly if one’s feet are slid into the Toe-asis™ Foot Warmer. It also isn’t as billowy and fluffy as other bags and is a little “crunchy,” perhaps owing to the ThermaCapture^TM lining which performs well for heat, less so for comfort.

Durability
The Mira HD showed no signs of wear and tear during the testing phase. The zipper did snag a few times although generally I would not expect there to be a problem with durability.