Warms root area approximately 10 – 20 degrees F over ambient temperature to improve germination process. Helps gardeners have better success rates with seedlings and cuttings. Perfect for one standard 10 in x 20 in propagation tray. Heavy-duty construction makes this mat very durable. More than 20% larger than competitive mats. This allows even warming of your entire tray. More consistent heating with fewer hot spots than other seedling heat mats. Ed Hume seal of approval. 20 W.