Here is a PHD triobag - this is in fact the protoype for this bag, bought direct from PHD some years ago.
It is a regular size. I used it for 10 nights doing the Tour Du Mont Blanc in Summer, it has always been used with a silk sleeping liner.
EDIT: I have had several requests to know the weight of this bag. I just used our digital luggage device, it is not the best and in fact I weighed it multiple times with the bag in the stuff sac and basically got a weight of 680g to 720g - so let's assume it's 700g for arguments sake. Google tells me a standard PHD stuff sac is approx. 50g. So I believe the bag is around 650g.
In terms of PHD bags and where it sits in termsnof it's lineup, I would place this unique bag close to their Minim 400
It is a very capable Summer / Alpine sleeping bag and you could likely use it down to 0 Celsius, but not warm enough for a Himalayan trek in my opinion.
The design enables you to sleep in 3 different ways according to external temps. See uploaded pics. Very clever.
Am selling as I now prefer sleeping blankets. This has no zip in order to be heat efficient.
PHD no longer sells these but you could argue this is like a PHD Minimus with a filler bag layer sewn into it.