"Soft leather" is a generic name given to the soft and supple leather qualities of certain leathers like lambskin and deerskin. When manufacturing soft leather, it's important for the tanner to make sure that the leather is as soft as possible.
Lambskin (also known as sheepskin) is an exceptionally wearable and soft leather. It’s composed of natural lightweight layers, giving it a distinctive, velvety texture. Because of its delicate structure, lambskin is treated less harshly in production than cowhide and requires more hand manipulation. This often results in lambskin being even more expensive than cowhide (which is why it’s generally reserved for premium leather products). Even though lambskin leather is thin and lightweight, it still does a good job of keeping cold out. On the other hand, this soft leather is more likely to stretch over time and also does not tolerate abuse as well as cow leather.
Deerskin is also softer than cowhide. Deerskin provides a natural resistance to cold and is even known to become warmer in cold weather and cooler in warm weather. The natural fibers in deerskin trap air inside, making the leather feel lighter and softer. It is surprisingly durable despite its softness. Its fibers are abrasion resistant and strong while remaining extraordinarily soft, but this soft leather does not stand up to wear and tear as well as cow leather.
It’s lightweight, comfortable, and wearable - and it can be a great option. Just don’t plan to beat it up.