No. The Lycra K9 Top Coat is made of lightweight Lycra that breathes quite easily. We are currently conducting a study of heat exposure with and without the K9 Top Coat at a major teaching Veterinary School. Preliminary results show that the K9 Top Coat does not cause ANY additional increase in core body temperature. So, as long as the dogs have ample water and shade, the K9 Top Coat is safe to use. It is our goal to produce the safest and most effective garment possible.