Hydrophilic–lipophilic balance

When creating suspensions, you may want to include a surfactant of a specifc Hydrophilic–lipophilic balance(HLB) value. What does the Hydrophilic–lipophilic balance value of a substance refer to? For suspensions, what Hydrophilic–lipophilic balance value and category of surfactant could you want to target? List two examples of surfactants of HLB values in this range.