The purchase of low-quality materials would most likely the result of a favorable materials price variance coupled with an unfavorable material usage variance. Material price variance is the difference between the cost and the budgeted and actual cost to obtain an object or materials, multiply to the total amount of the product purchased. They are what you called positive value of direct material price and negative value of direct material price. A positive value of direct material price variance is the one that is favorable and it means that the direct material was purchased for a lesser price than the standard price. A negative value of direct material price variance is the one that is unfavorable and it means that more than the expected price per unit is paid.