"Peat" is too broad a term to be useful. There are many types of peat, some of which have no sphagnum moss in them. Michigan peat, for example, is primarily a mucky mixture of decaying reeds and sedges. Sphagnum peat is harvested from the layers of partially decayed sphagnum moss below the surface of peat bogs, while sphagnum moss is harvested live from the surface:

{{gwi:10366}}

and is what you want for air layers.

Al

I have had very good luck using the sphagnum moss that Al describes when air layering Japanese maples.
Paul

Ditto!
My buddy air-layered three Japanese maple branches....and he discovered good roots in the moss
after the squirrels tore the air-layers apart... ;)

Josh