Reusable Therapy - Knee/Shoulder, 10" x 20" Hydrocollator HotPac & Units - Knee/Shoulder, 10" x 20" Hydrocollator HotPac Introduces Improved Moist Heat Technology with New, Synthetic Fabric Here's an easy way to provide moist heat therapy for patients-quickly, easily and targeted to any point of the body. HotPacs provide up to 30 minutes of moist heat per session. And now, they have a new synthetic covering that helps resist mold and mildew, dramatically increasing their lifespan. You'll get hundreds of treatments from each pack.