Returns to a factor means the increase in the Total Product (TP) per unit increase in the employment l of a variable factor, when the employment of other factors is kept constant.
Increasing Marginal Product leads to increasing returns to factor. In other words, when Total Product increases at an increasing rate, increasing returns to factor takes place. This can be explained with the help of following table.

Units of Variable Factor	Total Product	Marginal Product
0	0	0
1	10	10
2	22	12
3	36	14
4	52	16
5	70	18

In the table, MarginalProduct increases by employing an additional unit of variable factor. That is,Total Product is increasing at an increasing rate.Thus increasing MP leads to increasing returns of factor