Good or bad, but habits

public static class HexadecimalConverter
    {
        static readonly string[] fLookupTable;
        static HexadecimalConverter()
        {
            // Populates cache
            fLookupTable = new string[256];
            for (int i = 0; i < fLookupTable.Length; i++)
                fLookupTable[i] = i.ToString("X2");
        }

        // converts a byte array to an hexa string
        public static string ToHexString(byte[] bytes)
        {
            if (bytes == null || bytes.Length == 0) return "";

            char[] lChars = new char[bytes.Length * 2];
            for (int i = 0, j = -1; i < bytes.Length; i++)
            {
                string lHex = fLookupTable[bytes[i]];
                lChars[++j] = lHex[0];
                lChars[++j] = lHex[1];
            }

            return new string(lChars);
        }

        // Extension Method
        public static string ToHexadecimalString(this byte[] bytes)
        { 
            return HexadecimalConverter.ToHexString(bytes);
        }
    }