Considering the three types of Devil Fruits that has been explained are
1. Paramecia Type - where the user can get super human abilities and change their body parts into weapons, etc.
2. Zoan type - where the use can turn into a particular animal and inherit its abilities
3. Logia Type - where the user's body inherits a particular element and the body becomes like air which cannot be touched or damaged by non Haki users.
So what exactly is the type of Gomu Gomu no Mi?
It cannot be Zoan or Logia.
It's very close to a Paramecia but still doesn't have a logical explanation to be of Paramecia type!
So is it some special type of Devil Fruit?