We use cool shield bubble mailers. The bags are silver and are insulated and they are actually mailers. The bags help retain the temperature of the blood. We issue a lot of blood and sometimes when the blood is returned for whatever reason, the blood is too warm even though it was returned within 30 minutes. The price of the bags are not bad. You will have to order 5 cases at a time to get the discount price. The company is ULINE shipping supplies. Google cool shield bubble mailers to see what they look like. So far, we are pleased with them.