I'm seriously considering getting a Botrager Boulevard Fluid saddle. I sometimes ride in temps down to around 40F. What effect does cold weather have on fluid saddles?

Not sure I have ever seen a fluid saddle. plenty of gel saddles but not fluid. For a saddle you can have padding but you want it support your ischial tuberosity (sit bones) and not just sink in. If they aren't being well supported and you have to compress a lot of material in order to get supported you are creating pressure points which can cause pain.

My guess is if the saddle is fluid you would hope it is not like a water bed or something I don't think that would be very good down there. The Trek website doesn't really tell you what the fluid is or how it is contained or anything. Also that saddle is for a very upright bike so if you are not upright on your bike the saddle is probably going to be way too wide.

I'll bet that if you put something warm on it, like your butt, it will act normally in short order.

I'd imagine that at temperatures above freezing there would be little effect. But I'd submit this question to Trek for a more definitive answer.

I figured the same, at that temp, body heat would probably keep things pliable. I have asked Trek the question but they haven't gotten back to me yet. I had a gel saddle on my old bike that was quite comfortable. I don't know if the Boulevard has gel or "fluid", whatever it might be. It may just be a marketing term.

There is essentially zero chance that the "fluid" in this gel saddle is water based. While it might get stiffer in the cold, as Kontact so perceptively noted, the heat from your body would certainly bring it up to something much closer to room temp.

I had a sleeping setup in the back of a vehicle awhile ago. It was topped off with a memory foam mattress.

It was amazing how hard that mattress got in the cold.

I sank in and the spot I was laying on warmed up enough to still be comfortable. That’s on a 10 degree night with a nice sleeping bag between me and the pad.

I’m certain that the connection between your butt and this saddle on a 40 degree day is plenty warm. If I had to guess, I bet you won’t notice it.