Sealant in tubulars was a common thing years ago. I ran it regularly for races. I don’t think I had any punctures so I cannot comment from experience. I think the census was 50/50.
Would work sometimes.
I think the issues with success in running sealant in tubes is the pliability of the tube under pressure which can cause the puncture to not seal and potentially increase in size as the sealant flows to/thru it. Purely speculation and no testing or scientific backing to this.
But I did run it regularly in my Vittoria Cronos back in the day.

I’ve been running Caffelatex sealant in some latex tubes this year. Some things I’ve learned;

Sealant in a latex tube will lower the rate of pressure loss by about an order of magnitude. For what that’s worth.

Caffélatex states that sealant in tubes lasts longer than it does in tires. From their site:
- tubular (or inserted into a butyl/latex/polyurethane inner tube): up to 1 year
- tubeless tyre: 2-6 months
- tubeless-ready tyre: 1-4 months.

I can only speak to latex tubes but - if you deflate the tube all the way, either by neglecting to add air for a couple of months, or when moving the tube between tires, then the inside of the tube will immediately stick to itself. If you catch it within the first minute or so when it happens, you can re-inflate and the sides of the tube will separate with no apparent damage. I’ve done this a couple of times and the amount of force and stretch on the tube doesn’t seem risky to me

But beyond a minute or so, I can’t speak to whether you can safely separate the sides. I’m guessing you probably could for at least a few minutes longer, but I would toss a tube without hesitation if it sat empty for a day.

Just like with full tubeless, you have to avoid bleeding air when the valve is at the 6 o’clock position, or you can get sealant in the Presta valve and cause a clog or get the valve stuck open. Early on I had one flat due to this, where I hadn’t taken good precautions, and I got a leak that was too slow to detect. Since then I’ve been more careful and it’s never recurred.

I’ve never had a puncture so I can’t speak to how it seals. Based on what I’ve read, I don’t really expect it to work, but I hope to be pleasantly surprised.

Unless I actually experience them sealing a flat, I probably won’t do this again next year.

The one instance I might is for a long course A race, where I want to run latex tubes but it would be nice to not worry about losing air pressure over the day, and it would be worth having that tiny bit of extra defense against a flat.

I do worry that changing a flat would be harder, since sealant would presumably get all over the tire and rim.

Been doing this for years with my roadies and tri...have had several rides saved as it "sealed" as it should-only run pure tubeless in my MTB now...

Because sealant is a royal pain in the butt to deal with and live with.

The beauty of tubes is the simplicity. At least in my view. I've converted twice to tubeless, once in 2020 and earlier this year, and both times I bailed and went back to latex tubes within less than a year. They're just so easy to live with, and are basically just as fast for most of our purposes and if you're smart with tire/tube/pressure setups. Lower pressure benefits for tubeless are real, but I'm a smaller rider and don't do any gravel, and can ride low enough pressure with tubes that it's never been a problem for me.

It sounds like you are actually arguing tubes vs tubeless, not sealant vs no sealant in tubes. I've never had an issue with adding sealant to my latex tubes and been doing it for many years in multiple bikes. I'm still not interested in going tubleless for road or tri, but it's been good on my gravel bike and would definitely do it on a mt bike too.

Nope, I was still thinking about the pains of deciding when to top up, how much to put in/top up with, making sure the tube doesn't deflate and bind to itself because of sealant inside, cleaning up spills, etc. Sealant is messy/annoying stuff, and you have to monitor and maintain it inside of whatever you put it in whether tubes or tubeless tires. Certainly with tubes you are not dealing with the whole thing of seating tire beads but that's the only real difference.

None of those points have ever been an issue to me. Sealant in latex tubes lets them sit for weeks without deflating sufficiently to worry about the tube binding. I start the outdoor season with fresh tires and tubes so never need to "top off" sealant. I guess spills are an issue if you are clumsy or have never put sealant into a tube before but it's pretty simple - I just refill an old Stans 2oz bottle. The tip mates well with the opening on a valve stem with the core removed. Sounds like you are better of sticking with butyl tubes - probably shoud go with gatorskins too just to be safe :)

Hahah, well I have run conti 4000s then 5000s with latex tubes since I started cycling seriously 12 years ago, and have had only 5 flats ever in probably 35,000 miles of riding on that setup, so I think I'm ok! Lol.

I see the appeal that the sealant makes latex bleed less but I always pump tires to exact pressure before every ride so I doubt it would affect my routine anyways. But to each their own! Getting new tires and tubes is certainly a way to skirt the maintenance aspect, although I run latex tubes for many seasons in a row so only downside to that is a few extra bucks than you could otherwise spend. Tires can last more than a year for sure depending on your mileage so while you may save hassle with that approach, it certainly costs you some extra money to avoid sealant maintenance. But, it's all good and that's a totally good approach from that standpoint. Nothin like fresh tires, I get that!

I don't do it to avoid sealant maintenance. I definitely ride enough to need new tires at least once a year on both my road and tri bikes. I don't even ride that much IMO so I would assume most people should be swapping fresh rubber on a regular basis unless they are rotating a bunch of bikes maybe. On my race wheels I swap in new tubes at the beginning of the season regardless because they do sit for months and get bound up. I suppose I could avoid that by pumping them up one a month through the winter.

Nice. Yeah, a pump here or there thru the winter goes a good ways, but coat your tubes in baby powder before installing if you dont already. Prevents binding to tire and makes them easier to install/less likely to pinch as well. Some come pre powdered but even those I add a bit more.