Hi ajmellu7 and welcome to the Forum.
Yes, as others have said, its normal for hens to moult at this time of year. The days are short, and the lack of light heralds the end of the breeding season, so egg production declines markedly or stops altogether until after the winter solstice. By January, both the wild birds and domestic [poultry are getting sensitive to the increasing daylight, which stimulates their pituitary glands into hormonal activity, and they then prepare for a new laying season.
Whilst taking a break from laying, hens usually do their autumn moult, again in common with the wild birds. Old, tatty feathers are shed and new ones are grown to replace them, so they're all smart and ready for the next season. Apart from the lack of light, laying is also affected by moult, as it takes a lot of energy and protein to produce new feathers and there isn't enough to lay eggs as well. Some hens go nearly bald overnight, but most take it slower and it may be several weeks before the feathers are completely lost and replaced. Whilst moulting, they don't like being handled as the emerging feather stubs are very tender.
I'm a bit surprised that your 3-year-old hens haven't moulted before now, but I expect they are hybrids, bred to lay flat out for the first 2-3 seasons, and not to waste time having little 'holidays' where production would drop naturally. If this is so, and they've always laid well, then in the coming year you will probably notice a big drop in egg numbers, because they will have used up most of the egg cells they were born with. Purebred hens take life more in the slow lane, and as they don't lay so many eggs per year they tend to go on longer than hybrids. If your girls are actually hybrids, they would be for the chop at this point if they had ended up in a chicken farm. They should return to lay in the Spring and you will get a few more eggs next year, though these may become thinner shelled and develop other abnormalities such as wrinkled or misshapen shells.
I'm not greatly in favour of providing extra insulation for otherwise healthy moulting hens, unless the temperature is well below freezing maybe. So long as they have a dry, draughtproof coop, good ventilation is more important than anything, and adding extra bedding to the floor does nothing to make them warmer when they're perched.