I want buy Stop-A-Flat tube for my tire. Tire size is 26 x 2.25
Closest airless tube what I found, has size: 26 x 2.125
Is suitable that size for my 26 x 2.25 tire ?
Amazon web pages says
Stop-a-flat tubes are "Size Specific" to a tire and care should always be taken when matching the tube to the tyre.
Please note that the 1.75 sizes will fit a 1.90 standard tire.
So that's confusing. You'd really have to check with the manufacturer,
Bicycle tires vary in actual size for a nominal width specification by quite a lot, so if the solid inner tube needs to exactly fit the inside dimensions of the tire it will be difficult to get a match.
Personally, I would not use a product like this as I suspect they could negatively affect tire grip in a dangerous manner.