This is a Pompori's backpack carrier. M size I used it 3-4 times to take my guinea pig to the vet. The white cushion inside is attached to the bottom with Velcro. The bottom is sturdy, so it doesn't deform when you carry it on your back. However, it does sway quite a bit, so if you have a timid pet or are carrying an exotic animal like a guinea pig, you may need to carry it in front of you and support the bottom while moving, rather than carrying it on your back. However, while on the train, you don't need to hold the bottom, and you have both hands free, so it's a very convenient backpack for taking your pet to a slightly distant hospital, and it was a great help. Please refer to the last photo for the size. Shipping may be changed from Yamato to the post office depending on the timing.