Greetings, welcome to the Forums.
The deciduous trees known as Cottonwoods (Populus spp.), in the Willow Family (Salicaceae) are dioecious species. That is to say, male and female flowers are on separate plants. Trees sold as "cotton-less" Cottonwoods are male cultivars that will not produce fruits, seeds or the white, fluffy seed-hairs that give Cottonwoods their name.
Well-known "cotton-less" Cottonwood cultivars include Siouxland Eastern Cottonwood (Populus deltoides 'Siouxland')
and Robusta Canadian Poplar (Populus x canadensis 'Robusta'),
but there are other cultivars as well as innumerable unnamed seedlings that are also "cottonless".