Size regular. The Sea To Summit Alpine II sleeping bag is a beautifully-made and very technologically advanced down sleeping bag using very fine quality down. It use what Sea to Summit call a "3D nano shell", a very light layer of synthetic insulation between the down and the outer shell. This means that dew-point - where perspiration travelling outwards through the bags insulation from the person in the bag condenses - is in the synthetic outer layer and not in the down. This means the down stays drier and, hence, the bag warmer when used on multiple nights where you don't get the chance to dry the bag in the sun/warmth. The bag is rated by the EN 13537 standard as having a comfort level of -9 and a comfort limit of -15. I've slept in it without a tent happily at -15 on a number of nights, so think this is a pretty accurate indicator of the bags warmth.
Sea to Summit's page on this model with loads of technical information is here and my full review of the bag is on UKclimbing here. The bag comes with a lightweight compression sack, a big cotton sack for washing the bag in and a clever box-shaped 'bag' that stores the sleeping bag uncompressed but fits easily into a cupboard or similar.