I bought one of their ATV seat pads and it's actually pretty comfy and doesn't look too bad so thought I'd pass this on. With the exception of maybe needing one more strap to get it to lay down on the passenger platform the fit is pretty good too. It looks better than it does in the picture. Price is $19.95.

Is it air or foam?

Foam. I sat on it for a long drive in the car and it was great. Haven't taken it for any length of time on the bike yet.

I bought two of those same seat covers for my ATVs. Mostly to hold my but in place as I ride through snow drifts and mud. I have close to 1000 miles on mine. I used to ride about an hour before I had to stand up or get off due to a sore butt. Now I cam go a full day sitting on the seat, or at least until I have to stop for gas or open a gate.
One other thing, the fabric along with the squares help the seat breath better. My bottom doesn't get all sweaty any more.
I ride my quads in all kind of weather conditions... I rode 200 miles on back mountain trails in 100 degree weather.

Once the snow starts to fly again, I week report back on how I like it in the winter.

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You could very easily put that under the upholstery. All you need is a set of needle nose or something to pull the old staples, and a staple gun. You could probably have it done in less than 40 minutes. Just a thought.

Ah, the good old Stearns seat cover. I had one on my XT225. It helped for about 500 miles, by then it had completely compressed and was hard as a rock. There is only about 1/2" of foam on the XT's seat. I took it to an upholstery shop and had it rebuilt with about 2" of quality foam. That was over a year ago, and it is still way more comfortable than it was. But nothing I have ever ridden has been as comfortable as the Vulcan 750. It's an easy chair on wheels. Hundreds of miles without pain.