The recommended thickness for applying hard wax can vary based on personal preference and the specific area being waxed. In general, it is recommended to apply hard wax in a thick layer to ensure that it adheres properly to the hair and can be easily removed. However, in certain areas with thinner or more delicate skin, such as the upper lip or bikini area, a thinner layer of wax may be more appropriate to reduce the risk of irritation or discomfort. It's best to consult with a professional esthetician or waxing specialist for guidance on the appropriate thickness of hard wax to apply for your specific needs.