Ventis Gas Log Natural Gas Refresh Kit for Natural Gas log sets. The refresh kit will bring new life to your gas log sets. It offers a variety of different accessories to enhance the appearance of your fireplace. Simply add the different options included in the pack to help decorate around your log set. Easy to use, this accessory pack will provide years of hearth enhancements. Dual effect glowing embers is a vermiculite and rock wool mixture used to replace the original material to recreate those like new, realistic glowing embers. Silica sand maximizes diffusion of natural gas in the burner pan. Vermiculite replaces silica sand in propane installations, also increases glow with natural gas. Lava rock (also called volcanic cinders) is used to renew or replace the original rocks that came with the logs. Rock wool provides the bright ember effect with gas logs.