Consider $ T_1 \in \mathbb{C}^{d_1 \times \cdots \times d_k}$ as an order-$ k$ tensor of the format $ (d_1, \cdots , d_k)$ . Now, let $ T_2$ be an unfolding of $ T_1$ that is obtained by merging $ \mathbb{C}^{d_i}$ and $ \mathbb{C}^{d_j}$ into a single vector space $ \mathbb{C}^{d_id_j}$ , i.e. $ T_2$ is an order-$ (k-1)$ tensor of the format $ (d_1, \cdots , d_id_j, \cdots , d_k)$ , for $ i,j \in [k]$ . The question is what are the best general lower and upper bounds on the ratio $ \frac{R(T_1)}{R(T_2)}$ , where $ R(T_l)$ denotes the tensor rank of $ T_l$ , $ l=1,2$ ? Same question can also be asked about $ \frac{\underline{R}(T_1)}{\underline{R}(T_2)}$ , where $ \underline{R}$ denotes the border rank?