That's what mine is, gore-tex and thinsulate. A suit setup that combines both (most just use thinsulate) isn't cheap either. IIRC, it was near $700 between the jacket and the bib. It's definitely worth it though, the Gore-Tex really helps when things start to get stupid cold. My boots, as well as my gloves now, are also gore-tex and thinsulate.

We were out night riding one time and the temperature was -25*F. Our average speed was probably 30-40 mph, which means a windchill of about -60*F. Even at that temperature it kept me comfortable enough to keep riding. The only places I could remember being truly cold are my hands (which is why I went out and bought new gloves) and the parts of my face where the vents in the helmet are (I had to keep the vents open a little while we were moving or my glasses would fog up and the fog would freeze solid). Otherwise, I was surprised I wasn't colder.

Edit: On a side note to Sue.

I have ridden with a backpack and I don't like it, at least not for the type of trails we ride. This is for a few reasons:

First, most packs aren't designed to be used with a snow suit, the straps just aren't long enough (at least for someone my size, a small stature person might have an easier time). Wearing one feels like wearing a rubber band around your shoulders and back.

Second, riding a snowmobile on twisty trails is bumpy. Anything you have in the pack tends to slam into your back, no matter how tight you seem to have it cinched. It exacerbates the typical pain one experiences after a hard day of riding (shoulder pain, lower back pain, leg pain)

Finally, it throws off your weight distribution and turning ability. When riding you have to lean a certain way to keep things stable. It actually requires more effort that riding a typical two-wheeled vehicle, like a motorcycle or a dirt bike, because the wide track on the sled prevents it from leaning into corners as well as a bike.

Therefore, backpacks (or just about anything mounted high on the sled) tends to want to go the opposite way you need to lean. In the least, it means you'll have to use more energy not only fighting the sled to move how you want it, but fighting the pack as well. At worst, it could lead to your balance being compromised, which could lead to the rider being thrown off or having to ditch the sled to stop from rolling/crashing.

Instead, you'll find most riders prefer saddle bags. They make versions that can go over the back of the sled or over the center mounted fuel tank. They keep the added weight lower to the ground, which upsets the balance and handling of the machine less. With that in mind, you won't often find most day riders using them, as they typically try to ride as light and fast as possible. Saddle bags are more typical among those using the sled in a working fashion or those going on long trips that require the need to carry a lot of gear/supplies.