The playpen is traditionally made of wood and consists of a flat rectangular platform, usually square, with vertical strips on all sides so that the child can see it. The floor of the fence is usually a soft mat. The fenced wall is usually higher than the child's height to avoid injury; the playpen can also have a detachable cover. There are more modern and portable designs.

Modern playpens are portable and usually consist of basic metal and plastic support systems and mesh, soft plastic or nylon sides. An optional detachable cradle can be mounted on the top for the child to sleep or change until four months old. Some models have accessories such as cell phones, side pockets for toys and toys, replacement desk accessories, night lights, music boxes and clip-on adapters for CD players so that children can listen to music while sleeping or playing. Portable playpens come in different sizes, but most are expected to fold into small rolls for easy storage and transport. The difference between the fence and the playpen is small.

It is important to ensure that the fences used are safe for the child. This may be affected by product recalls when the baby fence has been purchased from second hand. Unsafe playpens can crash and can cause (possibly fatal) child injuries.