Nowadays, low expansion foam is again sub-divided into two types :
Primary aspirated foam : mixing of foam solution with air occurs inside the equipment, resulting in expansion ratios from 1:7 to 1:12 (e.g. foam branches, foam barrels)
Secondary aspirated foam : mixing of foam solution with air occurs after solution leaves the nozzle, resulting in comparatively lower expansion ratios i.e. 1:3 to 1:6 (e.g. Aqua foam nozzles, handline nozzles)
It may be noted that for secondary aspirated foam, only certain types of foam concentrates (AFFF, AR-AFFF, FFFP) will give proper results.