Underlying Asset Performance: BIEF39.SA tracks an index. The performance of the assets within that index directly impacts the ETF's price. Higher underlying asset values generally increase the ETF price.

Supply and Demand: Basic economics apply. Higher demand for BIEF39.SA pushes the price up, while increased selling pressure lowers it. ETF creation/redemption mechanisms help manage this.

Interest Rates: Interest rate changes can impact the attractiveness of fixed income assets within the underlying index, potentially affecting the ETF's price, particularly bond ETFs.

Economic Conditions: Overall economic health, inflation, and growth expectations influence the performance of the assets BIEF39.SA tracks, thereby affecting its price.

Currency Fluctuations: If the underlying assets are denominated in a different currency, exchange rate movements can impact the ETF's value when expressed in the trading currency.

Investor Sentiment: General market optimism or pessimism towards the specific asset class or region covered by BIEF39.SA can drive buying or selling activity, influencing its price.