Tell me about TT solid inners

Indeed – I find they add substantially to minimizing heat loss via convection.

I went with the TT semi solid inner for my Notch specifically because it blocks cool breezes and helps maintain a bit of warmth.

Before this I had a Copper Spur and Fly Creek which both have semi solid sides and I bought them both for the wind blocking properties. Specifically for me, it's wind blown fog that freezes you at night in an all mesh inner tent.

I've had a Scarp 1 with the semi solid interior and x-poles for 4 years now. The above comments are all correct. I've only used the x-poles in winter, not really needed for 3 season. I would highly recommend the semi interior. I have had all net interiors but they are not my cup of tea.

I agree with the previous posters. Solid inners are also much better than mesh at stopping condensation from dripping on you. I was in a single wall Moment when hurricane Irene hit the mountains of WV. There was some condensation dripping on me because of the heavy rain and wind. I did have the liner (like an inner fly), but I didn't bring it on that trip.

The top part of the Notch inner IS mesh. Been debating one for awhile.
I think the mesh will help with condensation, regardless.
The solid bottom portion means not having to lower the fly to avoid drafts in cold, windy conditions. That alone should eliminate a good bit of it, and the mesh will definitely keep frozen condensation from raining down on you if it does still occur.
It was "snowing" inside my Notch(fly w/groundsheet) when I bumped a trekking pole on a single digit morning early this year…

Only problem I have with the idea of using the solid inner is that it takes you back to having the same limited space as the net one. The Notch is a much more livable shelter when you just pitch the fly.

I also have the semi-solid inner on a Stratospire 2. My partner preferred it to keep direct breeze at bay and I like it. Super light, barely makes a difference there and I do believe it adds a slight advantage against the weather.

Don't the Notch and SS shelters have a 'storm pitch' where the fly goes right to the ground? If so, it doesn't seem like the solid inner would have much an advantage over the mesh (except possibly in the most extreme conditions). Am I wrong about this?

(Edit: the Duomid is considered a 4-season shelter and yet doesn't have a solid inner. Would a 'storm pitched' TT be any different?)

Rutherford,
I have used both solid and mesh TT inners in windy condition and on snow.
As you noted there are shelters that don't have an inner but are considered "4 season", it just depends on what you want/need as far as weather protection.
Some don't like the feel of air flow around them others don't notice.
This w/e I was camping on snow with a mate of mine.

I was inside the Scarp with solid inner he was , with his sister, inside a Scarp 2 with mesh.
I had recommended the mesh inner to him because he sweats a lot so he can benefit from extra air flow.
The first night, forgetting about the lower fly and the solid inner AND to open up the vents (so much for my expertise…) I had a lot of condensation ,including a damp (on the outside) sleeping bag still no drips on me but even the inner was wet.
My mate had condensation under the fly but not on the inner.
( we had some wind early in the night so 'ventilation" did not come to mind. It became perfectly still later on the night…)
The second night having recovered my senses I opened up the vents and kept the doors of the inner partially open so I had just parts of the fly wet with condensation.
As a comparison most other tents around us (about 12) were coated with a thicker layer of frost and rather droopy so we did rather well .
So compering it with my use of the Notch/mesh and Moment/hybrid (no inner, the Scarp solid inner does feel warmer but you need to keep in mind allowing air flow when not windy.

Both my Scarp 2 and Moment DW have the ripstop inner W/ netting top panels. I got 'em for 4 season camping.

The Scarp 2 gets some frost on the inside of the fly, as do all double wall tents but I had the bottom end vents and top vents open so it was not anything bad.

This winter I'll see how the Moment DW does but I think it will be fine compared to my old single wall Moment even with the optional liner.

Blowing sand in Utah's Grand Escalante area was a real problem in the Moment single wall with its mesh just above the bathtub floor.and total mesh inner door. That will not be the case with the new Moment DW.

Has anyone tried to use a lightweight bivy inside of a a solo TT outer (Moment, Notch, SS fly) in winter? Would this give similar benefits to the solid inner?

It seems like that would be a great setup for reducing heat loss due to convection.

It will give the benefit of adding some warmth and as well, protecting from ground water and bugs. However, all the downsides of using a bivy, which are numerous, would still apply for minimal weight loss compared to the dedicated inner (in my opinion).

I made my own bivy to be used inside the Notch but although it is larger than my purchased LW type bivy it is still too small to hold a thick mat.
An advantage with the Scarps is that you can fit an extra person if using them , so the Scarp 1 will hold 2 and the Scarp 2 will hold 3.